41 results on '"Yang, Xin-yu"'
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2. Stabilities of group-III phosphide (MP, M = B, Al, Ga and In) monolayers in oxygen and water environments
- Author
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Jia-Hui Li, Yang-Xin Yu, and Jie Wu
- Subjects
Materials science ,Annealing (metallurgy) ,Phosphide ,Intermolecular force ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Oxygen ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Monolayer ,Photocatalysis ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Group-III phosphide (MP, M = B, Al, Ga and In) monolayers have promising applications in photocatalysis, nanoelectronics and optoelectronics. Their stabilities in oxygen and water environments are crucial to their practical applications. In order to investigate the stabilities of the MP monolayers, density functional theory calculations combined with ab initio molecular dynamics (AIMD) simulations were performed to illustrate their interactions with oxygen and water molecules. It was found that an oxygen molecule spontaneously dissociates on the AlP, GaP and InP monolayers. In the meantime, the corresponding monolayer structures are severely distorted after annealing. In contrast, BP monolayer is stable in the oxygen environment due to a high dissociative barrier of 0.89 eV. We found that a water molecule dissociates on AlP monolayer with a dissociative energy barrier of 0.42 eV, but it can be stably adsorbed on the BP, GaP and InP monolayers without the breakage of O-H bonds. Nevertheless, with the increase of the number of water molecules, the formed intermolecular H-bonding can promote interactions between water molecules and the monolayers, leading to structural distortion in the GaP and InP monolayers. When putting a water molecule near the oxygen molecule, the oxidation barrier of the BP monolayer is reduced to 0.75 eV, which is still high enough to maintain its stable state. This investigation theoretically provides environmental conditions for the experimental fabrication and practical application of semiconductor monolayers.
- Published
- 2020
3. N 2 O adsorption and decomposition over ZnO(0001) doped graphene: Density functional theory calculations
- Author
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Yujun Wang, Reza Gholizadeh, and Yang-Xin Yu
- Subjects
Reaction mechanism ,Materials science ,Inorganic chemistry ,Ab initio ,General Physics and Astronomy ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Decomposition ,0104 chemical sciences ,Surfaces, Coatings and Films ,Catalysis ,Adsorption ,Transition metal ,Physical chemistry ,Molecule ,Density functional theory ,0210 nano-technology - Abstract
The main objective of this study is density functional theory investigations on adsorption and decomposition of N 2 O on ZnO(0001)-G nanocomposite. The adsorption and decomposition of small molecules on the magnetic oxides containing transition metals are relatively rare due to the modeling difficulties using current density functional approximations. A molecular modeling of the reaction mechanism was studied in this work through ab initio modeling of the catalytic adsorption and decomposition of N 2 O on ZnO(0001)-G. DFT was used to study the molecular mechanism of conceivable elementary steps of the decomposition of N 2 O over the most stable (0001) surface. Three reactions including the N 2 O bond cleavage, the oxygen atom transfer, forming a surface peroxy group O 2 2− were studied. The horse-like (N N O), parallel (N N O) and lying-atop-011 (O N N) with all three atoms of the N 2 O molecule interacting with the surface have been found as more stable adsorption forms, which have adsorption energies of −0.27, −0.23 and −0.23 eV, respectively. The activation energies of the N 2 O decomposition through mentioned reactions were found to be 2.73, 0.48 and 0.63 eV, respectively. The obtained results reveal that ZnO(0001)-G is not only an efficient but also a green catalyst in comparison with others such as Mn-G.
- Published
- 2017
4. Identification of the different contributions of pseudocapacitance and quantum capacitance and their electronic-structure-based intrinsic transport kinetics in electrode materials
- Author
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Lirong Zhang, Yang-Xin Yu, Wenhui Zhang, Xitian Zhang, and Jing Wen
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Materials science ,Kinetics ,General Physics and Astronomy ,Boundary (topology) ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Pseudocapacitance ,0104 chemical sciences ,Quantum capacitance ,Chemical physics ,Density functional theory ,Graphite ,Physical and Theoretical Chemistry ,0210 nano-technology ,Voltage - Abstract
The boundary between quantum capacitance and pseudocapacitance is blurred due to their similarity in electronic populations. Here we propose the rules to classify the contributions of quantum capacitance and pseudocapacitance and their effects on the intrinsic ion transport kinetics based on the applied voltages and electronic structures. Systems including graphite, LiFePO4, LiTiS2, LiCoO2, and Ti3C2Tx MXene are employed to illustrate their different intrinsic kinetics according to the classifications based on the density functional theory calculations and the reported experimental measurements. These results can facilitate the step to screen the electrode materials with different kinetics through calculations.
- Published
- 2021
5. High storage capacity and small volume change of potassium-intercalation into novel vanadium oxychalcogenide monolayers V2S2O, V2Se2O and V2Te2O: An ab initio DFT investigation
- Author
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Yang-Xin Yu
- Subjects
Materials science ,Intercalation (chemistry) ,Ab initio ,General Physics and Astronomy ,Potassium-ion battery ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Exfoliation joint ,0104 chemical sciences ,Surfaces, Coatings and Films ,Adsorption ,Standard electrode potential ,Monolayer ,Physical chemistry ,Density functional theory ,0210 nano-technology - Abstract
A new category of two-dimensional electrode materials, i.e., V2Ch2O (Ch = S, Se and Te) monolayers was explored for K-ion batteries (PIBs) based on principle of chemical exfoliation, density functional theory and ab initio molecular dynamics simulations. The V2Ch2O monolayers show low cleavage energies and excellent thermal, dynamical and mechanical stabilities. Adsorption energies of a potassium atom on the V2Ch2O monolayers are exothermic, which are of benefit to prevent forming dendrites. The existence of electrode potentials substantially decreases the diffusion barriers of potassium atoms on the three V2Ch2O monolayers. The V2Ch2O monolayers are able to maintain their metallic characteristics and single surface phase during the whole K-intercalation process, avoiding the decrease in electronic conductivity and the appearance of potential hysteresis. The theoretical specific capacities of the V2S2O, V2Se2O and V2Te2O monolayers are predicted to be 883.6, 583.1 and 431.0 mAh g−1, respectively, and the corresponding average open-circuit voltages are 0.449, 0.390 and 0.293 V, respectively. The maximum percentage changes in lattice parameters are 4.21%, 6.07% and 7.26% for the V2S2O, V2Se2O and V2Te2O monolayers, respectively. All the calculated properties indicate that the V2Ch2O monolayers are promising electrode materials for PIBs with high capacities and long cycle lives.
- Published
- 2021
6. Molecular dynamics simulations of stability at the early stages of silica materials preparation
- Author
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Yang-Xin Yu, Yujun Wang, and Reza Gholizadeh
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Chemistry ,Organic Chemistry ,Physics::Optics ,02 engineering and technology ,Dihedral angle ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Radial distribution function ,01 natural sciences ,Electric charge ,Force field (chemistry) ,0104 chemical sciences ,Analytical Chemistry ,Condensed Matter::Soft Condensed Matter ,Inorganic Chemistry ,Mean squared displacement ,Molecular dynamics ,symbols.namesake ,Chemical physics ,Computational chemistry ,symbols ,Density functional theory ,van der Waals force ,0210 nano-technology ,Spectroscopy - Abstract
The main objective of this article is the Molecular dynamics simulations of stability phenomenon at the early stages of silica production in a colloidal solution. The Dreiding force field used during the whole calculation for the search of all bonding, angle, dihedral, inversion potential sets for a given configuration. For studying the stability phenomenon, two scenarios are specified: (1) The diameter of silica nanoparticles in each simulation box is the same while initial distances of two silica nanoparticles are different (system I), (2) The initial distance between two silica nanoparticles in each simulation box is the same while silica nanoparticles diameters are different (system II). The charge of atoms in silica nanoparticles determined using density functional theory calculations (Dmol 3 ). The Born repulsion forces were predominant rather than the van der Waals attraction forces. Furthermore, trajectories, mean squared displacements, radial distribution functions, and electrical charges of silica nanoparticles are determined. The displacement of silica nanoparticles was negligible which demonstrates that atoms could not approach more close. The studied colloidal solution was stable regard to the results of molecular dynamics simulations.
- Published
- 2017
7. Prediction of Mobility, Enhanced Storage Capacity, and Volume Change during Sodiation on Interlayer-Expanded Functionalized Ti3C2 MXene Anode Materials for Sodium-Ion Batteries
- Author
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Yang-Xin Yu
- Subjects
Battery (electricity) ,Materials science ,Diffusion ,Intercalation (chemistry) ,Ab initio ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Anode ,General Energy ,Adsorption ,Chemical engineering ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,MXenes - Abstract
Sodium storage capacity, mobility, and volume change during sodiation on the surfaces of interlayer-expanded Ti3C2 MXenes are investigated using ab initio density functional theory. The theoretical results reveal that the interlayer-expanded bare, F-, O-, and OH-functionalized Ti3C2 MXenes exhibit low barriers for sodium diffusion and small changes of lattice constant during sodiation. In addition, enlarged interlayer distance enables the stable multilayer adsorption on the bare and O-functionalized Ti3C2 MXenes and therefore significantly enhances their theoretical capacities. Both bare and O-functionalized Ti3C2 MXenes are predicted to be prospective anode materials for sodium-ion batteries with high theoretical capacities, fast discharge/charge rates, and good cycling performances. The present results provide a new route to improve the battery performances of anode materials based on MXene intercalation hosts.
- Published
- 2016
8. Adsorption and substitution effects of Mg on the growth of calcium sulfate hemihydrate: An ab initio DFT study
- Author
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S.C. Hou, Lan Xiang, Yang-Xin Yu, and Yan Xin
- Subjects
Chemistry ,Whiskers ,Doping ,Ab initio ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Ion ,symbols.namesake ,Crystallography ,Adsorption ,Atom ,symbols ,Density functional theory ,van der Waals force - Abstract
Calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O, CSH) whiskers with high aspect ratio are promising reinforce materials which have drawn much attention. In order to obtain high quality CSH materials, effect of Mg 2+ ions on properties of the (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes of CSH is investigated using an ab initio density functional theory (DFT) with a van der Waals (vdW) dispersion-correction. The computed results show that strong adsorption and substitution effects take place between Mg 2+ ion and (2 0 0) 1 plane. The adsorption energies of an Mg 2+ ion on the (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes are −0.066, −0.571 and −0.047 eV, respectively. An insight into the electrostatic potential of pristine CSH planes has demonstrated that the (2 0 0) 1 plane is much more negatively charged than the (0 0 2) and (2 0 0) 2 planes. The energies of the substitution of a Ca atom with an Mg atom on the CSH (0 0 2), (2 0 0) 1 and (2 0 0) 2 planes are 1.572, 0.063 and 1.349 eV, respectively. It is found that Ca atoms on the (2 0 0) 1 plane are relatively easy to be substituted by Mg atoms. The calculation results of a Ca 2+ ion adsorption on the Mg-doped (2 0 0) 1 plane indicate that the adsorption energies increase apparently as the doping ratio varies from 0 to 1.0. Compared with K + , Na + and Al 3+ ions, Mg 2+ ion is the most promising additive to promote the growth of CSH along c axis.
- Published
- 2015
9. N2O + CO reaction over Si- and Se-doped graphenes: An ab initio DFT study
- Author
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Yang-Xin Yu and Reza Gholizadeh
- Subjects
Graphene ,Ab initio ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Activation energy ,Condensed Matter Physics ,Chemical reaction ,Surfaces, Coatings and Films ,law.invention ,Catalysis ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Computational chemistry ,law ,Physics::Atomic and Molecular Clusters ,symbols ,Physical chemistry ,Density functional theory ,Physics::Chemical Physics ,van der Waals force ,Carbon monoxide - Abstract
Catalytic conversion of non-CO2 green house gases and other harmful gases is a promising way to protect the atmospheric environment. Non-metal atom-doped graphene is attractive for use as a catalyst in the conversion due to its unique electronic properties, relatively low price and leaving no burden to the environment. To make an attempt on the development of green catalysts for the conversion, ab initio density functional theory is used to investigate the mechanisms of N2O reduction by CO on Si- and Se-doped graphenes. We have calculated the geometries and adsorption energies of reaction species (N2O, CO, N2 and CO2) as well as energy profiles along the reaction pathways. The activation energies of N2O decomposition and CO oxidation on both Si- and Se-doped graphenes have been obtained. Our calculated results indicate that the catalytic activity of Si-doped graphene is better than the Fe+ in gas phase and comparable to the single Fe atom embedded on graphene. In the calculations, we found that van der Waals interactions and zero-point energy are two non-negligible factors for the predictions of the activation energies. Further discussion shows that Si-doped graphene can be one of efficient green catalysts for conversion of the airborne pollutants and Se-doped graphene can be a candidate for oxidizing CO by atomic oxygen.
- Published
- 2015
10. Density functional theory study on ion adsorption and electroosmotic flow in a membrane with charged cylindrical pores
- Author
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Yuan-Xiang Zheng, Yan Xin, and Yang-Xin Yu
- Subjects
Valence (chemistry) ,Chemistry ,Monte Carlo method ,Biophysics ,Analytical chemistry ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Ion ,Adsorption ,Chemical physics ,Electric field ,Density functional theory ,Surface charge ,Physical and Theoretical Chemistry ,0210 nano-technology ,Molecular Biology - Abstract
Ion adsorption and electroosmotic flow induced by an external electric field have a variety of practical applications, especially for membrane technology. In this work, a partially perturbative density functional theory (DFT) based on the modified fundamental measure theory was applied to investigate the ion density distributions and partitions in a charged cylindrical pore. Different types of electrolyte solutions, including both charge symmetric and asymmetric, were examined using the proposed theory with various pore diameters, bulk densities, ion valencies and surface charge densities. The ion concentration profiles calculated with the theory exhibit good agreements with the results of the Monte Carlo simulations, while the results of the Poisson–Boltzmann equation deviate greatly especially for the high valence electrolytes in narrow cylindrical pores. Some interesting phenomena discovered in both experiments and simulations, such as the reverse distribution of the ions and charge inversion, ...
- Published
- 2015
11. Work Functions of Pristine and Heteroatom-Doped Graphenes under Different External Electric Fields: An ab Initio DFT Study
- Author
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Reza Gholizadeh and Yang-Xin Yu
- Subjects
Condensed matter physics ,Graphene ,Chemistry ,Doping ,Ab initio ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Dipole ,General Energy ,law ,Electric field ,Physics::Atomic and Molecular Clusters ,Density of states ,Density functional theory ,Work function ,Physical and Theoretical Chemistry - Abstract
Low contact barrier electrodes and various field-emitting devices require a tunable work function, and graphene is a dream material for these applications. In this work, the theoretical investigations on the variation of the work function for monolayer graphene doped with different kinds of atoms from groups IIA–VIA of the Periodic Table are reported. The geometry, density of states, dipole moment, and work function of each heteroatom-doped graphene are calculated using ab initio density functional theory with a dispersion correction. The obtained formation energy of the heteroatom-doped graphenes is in the order: N < B < P < O < S < Si < As < Se < Ge < Al < Ga. The work functions without an electric field abide by a periodic law in terms of doping atoms except for O-doped graphene. The calculated results demonstrate that the work functions of all heteroatom-doped graphenes are a linear function of the applied external electric field intensity, and the slopes of the lines deviate from the ideal value to a...
- Published
- 2014
12. An important atomic process in the CVD growth of graphene: Sinking and up-floating of carbon atom on copper surface
- Author
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Yue Yu, Mwenya Trevor, Yingfeng Li, Fan Bai, Yang-Xin Yu, Meicheng Li, and Gu Tiansheng
- Subjects
Materials science ,Dimer ,General Physics and Astronomy ,chemistry.chemical_element ,Nanotechnology ,law.invention ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Adsorption ,law ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,Physics::Chemical Physics ,Condensed Matter::Quantum Gases ,Graphene ,Relaxation (NMR) ,Tetravalence ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Copper ,Surfaces, Coatings and Films ,chemistry ,Chemical physics ,Density functional theory ,Carbon - Abstract
By density functional theory (DFT) calculations, the early stages of the growth of graphene on copper (1 1 1) surface are investigated. At the very first time of graphene growth, the carbon atom sinks into subsurface. As more carbon atoms are adsorbed nearby the site, the sunken carbon atom will spontaneously form a dimer with one of the newly adsorbed carbon atoms, and the formed dimer will up-float on the top of the surface. We emphasize the role of the co-operative relaxation of the co-adsorbed carbon atoms in facilitating the sinking and up-floating of carbon atoms. In detail: when two carbon atoms are co-adsorbed, their co-operative relaxation will result in different carbon–copper interactions for the co-adsorbed carbon atoms. This difference facilitates the sinking of a single carbon atom into the subsurface. As a third carbon atom is co-adsorbed nearby, it draws the sunken carbon atom on top of the surface, forming a dimer. Co-operative relaxations of the surface involving all adsorbed carbon atoms and their copper neighbors facilitate these sinking and up-floating processes. This investigation is helpful for the deeper understanding of graphene synthesis and the choosing of optimal carbon sources or process.
- Published
- 2013
13. Adsorption of carbon monoxide on Ag(I)-ZSM-5 zeolite: An ab initio density functional theory study
- Author
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Jianguo Mi, Zhen-Zhen Qiu, and Yang-Xin Yu
- Subjects
Coordination number ,Inorganic chemistry ,Ab initio ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Bond length ,chemistry.chemical_compound ,Adsorption ,chemistry ,Atom ,Physical chemistry ,Density functional theory ,Zeolite ,Carbon monoxide - Abstract
Adsorption of carbon monoxide on different Ag + -exchange sites of Ag–ZSM-5 zeolite has been investigated using density functional theory. The coordination and local geometry of the Ag + ion in Ag–ZSM-5 as well as adsorption structures and energies of CO adsorbed on these sites are explored extensively. The structure of Ag + -exchange sites, location of the Al atom on the T site, and number of the Al atoms contained in the sites are considered in the theoretical calculations. The calculated results show that the Ag O coordination number of two is strongly preferred before and after CO adsorption. The Ag O bond lengths are in a broad range of 2.2–2.9 A, and the Ag C bond lengths for CO adsorbed on Ag–ZSM-5 zeolite are calculated to be 2.0–2.2 A. Both Ag O and Ag C bond lengths for CO–Ag–ZSM-5 complex are longer than those for CO–Cu–ZSM-5 complex. The calculated adsorption energy of CO adsorbed on the I2 sites is between 28.5 and 29.6 kcal/mol, and that on the Z5, Z6, M5 and M6 sites containing one Al atom on the T position is between 11.3 and 18.9 kcal/mol whereas the calculated adsorption energy of CO adsorbed on the M7 site containing one Al atom is 19.9 kcal/mol. The introduction of the two Al atoms to the Ag + -exchange site results in a reduction of CO adsorption energy. In general, the adsorption energy of CO on Ag–ZSM-5 is lower than that on Cu–ZSM-5. The predicted coordination of the Ag + ion, bond lengths of Ag O and Ag C as well as adsorption energy are in accord with available experimental results.
- Published
- 2012
14. Excellent Infrared Nonlinear Optical Crystals BaMO(IO3)5 (M = V, Ta) Predicted by First Principle Calculations
- Author
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Mengqi Cui, Mingde Qin, Yang-Xin Yu, Xiang Li, Meicheng Li, Yingfeng Li, Lihua Chu, Hejin Yan, and Bing Jiang
- Subjects
Materials science ,Absorption spectroscopy ,Infrared ,02 engineering and technology ,010402 general chemistry ,Nonlinear optical crystal ,lcsh:Technology ,01 natural sciences ,Molecular physics ,Article ,Electronegativity ,SOJT ,General Materials Science ,lcsh:Microscopy ,density functional theory ,lcsh:QC120-168.85 ,Ionic radius ,lcsh:QH201-278.5 ,lcsh:T ,second harmonic generation ,Second-harmonic generation ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,laser damage threshold ,lcsh:TA1-2040 ,First principle ,lcsh:Descriptive and experimental mechanics ,Density functional theory ,lcsh:Electrical engineering. Electronics. Nuclear engineering ,lcsh:Engineering (General). Civil engineering (General) ,0210 nano-technology ,lcsh:TK1-9971 - Abstract
Two nonlinear optical crystals, BaVO(IO3)5 and BaTaO(IO3)5, are designed by substituting Nb with V and Ta, respectively, in BaNbO(IO3)5, which is itself a recently synthesized infrared nonlinear optical (NLO) material. The designs of BaVO(IO3)5 and BaTaO(IO3)5 from BaNbO(IO3)5 are based on the following motivation: BaVO(IO3)5 should have a larger second-harmonic generation (SHG) coefficient than BaNbO(IO3)5, as V will result in a stronger second-order Jahn-Teller effect than Nb due to its smaller ion radius, at the same time, BaTaO(IO3)5 should have a larger laser-damage threshold, due to the fact that Ta has a smaller electronegativity leading to a greater band-gap. Established on reliable first-principle calculations, it is demonstrated that BaVO(IO3)5 has a much larger SHG coefficient than BaNbO(IO3)5 (23.42 ×, 10&minus, 9 vs. 18.66 ×, 9 esu), and BaTaO(IO3)5 has a significantly greater band-gap than BaNbO(IO3)5 (4.20 vs. 3.55 eV). Meanwhile, the absorption spectra and birefringences of both BaVO(IO3)5 and BaTaO(IO3)5 are acceptable for practice, suggesting that these two crystals can both be expected to be excellent infrared NLO materials.
- Published
- 2018
15. Density functional study on the osmotic coefficient for the DNA–electrolyte solutions
- Author
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Yang-Xin Yu, Ke Wang, and Guang-Hua Gao
- Subjects
Chemistry ,General Chemical Engineering ,Monte Carlo method ,General Physics and Astronomy ,Thermodynamics ,Hard spheres ,Electrolyte ,Time-dependent density functional theory ,Ion ,symbols.namesake ,Helmholtz free energy ,symbols ,Osmotic coefficient ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
The ion density profiles and mean electrostatic potentials around DNA from the Monte Carlo simulations are compared with the predictions of the Poisson–Boltzmann equation and the density functional theory. The DNA molecules are modeled as a charged cylinder while the ions are represented as charged hard spheres with different diameter. In the density functional theory, the Helmholtz free energy functional due to hard-sphere repulsion and electrostatic interaction are obtained from the modified fundamental measure theory and a quadratic functional Taylor expansion, respectively. The results show that due to the inclusion of the ion–ion correlation, the density functional theory is more accurate than the Poisson–Boltzmann equation. The density functional theory gives accurate ion structures and mean electrostatic potentials near the surface of DNA. When the established density functional theory is combined with the cell model, the osmotic coefficients of aqueous DNA–electrolyte solutions can be predicted. The results show that the DFT-cell model captures the essential features of the experimental osmotic coefficient, but fails to give a quantitative description. Possible reasons for this discrepancy are discussed.
- Published
- 2007
16. Density Functional Theory Study on the Structure and Capillary Phase Transition of a Polymer Melt in a Slitlike Pore: Effect of Attraction
- Author
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Xiaolin Wang, Guang-Hua Gao, and Yang-Xin Yu
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chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Phase transition ,Capillary action ,Thermodynamics ,Polymer ,Radial distribution function ,Surfaces, Coatings and Films ,Condensed Matter::Soft Condensed Matter ,Correlation function (statistical mechanics) ,symbols.namesake ,chemistry ,Computational chemistry ,Helmholtz free energy ,Materials Chemistry ,symbols ,Density functional theory ,Perturbation theory (quantum mechanics) ,Physical and Theoretical Chemistry - Abstract
A density functional theory is proposed to investigate the effects of polymer monomer-monomer and monomer-wall attractions on the density profile, chain configuration, and equilibrium capillary phase transition of a freely jointed multi-Yukawa fluid confined in a slitlike pore. The excess Helmholtz energy functional is constructed by using the modified fundamental measure theory, Wertheim's first-order thermodynamic perturbation theory, and Rosenfeld's perturbative method, in which the bulk radial distribution function and direct correlation function of hard-core multi-Yukawa monomers are obtained from the first-order mean spherical approximation. Comparisons of density profiles and bond orientation correlation functions of inhomogeneous chain fluids predicted from the present theory with the simulation data show that the present theory is very accurate, superior to the previous theory. The present theory predicts that the polymer monomer-monomer attraction lowers the strength of oscillations for density profiles and bond orientation correlation functions and makes the excess adsorption more negative. It is interesting to find that the equilibrium capillary phase transition of the polymeric fluid in the hard slitlike pore occurs at a higher chemical potential than in bulk condition, but as the attraction of the pore wall is increased sufficiently, the chemical potential for equilibrium capillary phase transition becomes lower than that for bulk vapor-liquid equilibrium.
- Published
- 2006
17. Structure and Adsorption of A Hard-Core Multi-Yukawa Fluid Confined in A Slitlike Pore: Grand Canonical Monte Carlo Simulation and Density Functional Study
- Author
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Fengqi You, Yiping Tang, Yang-Xin Yu, Guang-Hua Gao, and Yi Gui Li
- Subjects
Surface (mathematics) ,Chemistry ,Monte Carlo method ,Yukawa potential ,Thermodynamics ,Surfaces, Coatings and Films ,symbols.namesake ,Grand canonical ensemble ,Correlation function (statistical mechanics) ,Adsorption ,Helmholtz free energy ,Materials Chemistry ,symbols ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
Because of the increasing interest in studying the phenomenon exhibited by charge-stabilized colloidal suspensions in confining geometry, we present a density functional theory (DFT) for a hard-core multi-Yukawa fluid. The excess Helmholtz free-energy functional is constructed by using the modified fundamental measure theory and Rosenfeld's perturbative method, in which the bulk direct correlation function is obtained from the first-order mean spherical approximation. To validate the established theory, grand canonical ensemble Monte Carlo (GCMC) simulations are carried out to determine the density profiles and surface excesses of multi-Yukawa fluid in a slitlike pore. Comparisons of the theoretical results with the GCMC data suggest that the present DFT gives very accurate density profiles and surface excesses of multi-Yukawa fluid in the slitlike pore as well as the radial distribution functions of the bulk fluid. Both the DFT and the GCMC simulations predict the depletion of the multi-Yukawa fluid near a nonattractive wall, while the mean-field theory fails to describe this depletion in some cases. Because the simple form of the direct correlation function is used, the present DFT is computationally as efficient as the mean-field theory, but reproduces the simulation data much better than the mean-field theory.
- Published
- 2005
18. Density functional for structures of colloids confined in a slit-like pore
- Author
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Sheng Fu, Fengqi You, Guang-Hua Gao, and Yang-Xin Yu
- Subjects
Chemistry ,digestive, oral, and skin physiology ,Monte Carlo method ,Yukawa potential ,Radial distribution ,Condensed Matter Physics ,Molecular physics ,Condensed Matter::Soft Condensed Matter ,Colloid ,symbols.namesake ,Colloidal particle ,Quantum mechanics ,Desorption ,Helmholtz free energy ,symbols ,General Materials Science ,Density functional theory - Abstract
A density functional theory is applied to calculating the local density profiles of colloids confined in a slit-like pore as well as the radial distribution functions of bulk colloids. The interaction between the colloidal particles is described using a hard-core Yukawa model. The excess Helmholtz energy functional is a combination of the modified fundamental measure theory of Yu and Wu (2002) for the hard-core contribution and a corrected mean-field theory for the attractive contribution. Comparison with the results from the Monte Carlo simulations shows that the corrected theory improves the density profiles of colloids in the vicinity of contact over the original mean-field theory. Both the present corrected theory and simulations suggest that there are depletion and desorption for the colloid with strong attraction between particles at low temperature.
- Published
- 2005
19. Density-functional theory of spherical electric double layers and ζ potentials of colloidal particles in restricted-primitive-model electrolyte solutions
- Author
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Jianzhong Wu, Yang-Xin Yu, and Guang-Hua Gao
- Subjects
Classical mechanics ,Chemical physics ,Chemistry ,General Physics and Astronomy ,Charge density ,Ionic bonding ,Density functional theory ,Electrolyte ,Physical and Theoretical Chemistry ,Poisson's equation ,Electrostatics ,Boltzmann equation ,Ion - Abstract
A density-functional theory is proposed to describe the density profiles of small ions around an isolated colloidal particle in the framework of the restricted primitive model where the small ions have uniform size and the solvent is represented by a dielectric continuum. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The theoretical predictions are in good agreement with the results from Monte Carlo simulations and from previous investigations using integral-equation theory for the ionic density profiles and the zeta potentials of spherical particles at a variety of solution conditions. Like the integral-equation approaches, the density-functional theory is able to capture the oscillatory density profiles of small ions and the charge inversion (overcharging) phenomena for particles with elevated charge density. In particular, our density-functional theory predicts the formation of a second counterion layer near the surface of highly charged spherical particle. Conversely, the nonlinear Poisson-Boltzmann theory and its variations are unable to represent the oscillatory behavior of small ion distributions and charge inversion. Finally, our density-functional theory predicts charge inversion even in a 1:1 electrolyte solution as long as the salt concentration is sufficiently high.
- Published
- 2004
20. Density functional study of the adsorption and separation of hydrogen in single-walled carbon nanotube
- Author
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Guang-Hua Gao, Chong Gu, and Yang-Xin Yu
- Subjects
Nanotube ,Hydrogen ,Renewable Energy, Sustainability and the Environment ,Chemistry ,Energy Engineering and Power Technology ,Thermodynamics ,chemistry.chemical_element ,Monoxide ,Carbon nanotube ,Condensed Matter Physics ,Separation process ,law.invention ,Hydrogen storage ,Fuel Technology ,Adsorption ,law ,Density functional theory ,Physics::Chemical Physics - Abstract
In this work, we report an investigation by means of density functional theory (DFT) of the adsorption of hydrogen and the separation of hydrogen–carbon monoxide mixture in an isolated single-walled carbon nanotube. The theory is based on a perturbative construction of free energy functional for inhomogeneous pure fluid and binary fluid mixture. The reformulated Rosenfeld's fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state proposed by Yu and Wu (J. Chem. Phys. 117 (2002) 10156) is applied to represent the pure and binary hard-sphere repulsive interaction, and Weeks–Chandler–Andersen perturbation theory is used to build the attractive contribution. The density profiles in three sizes of tubes at 300 K and reduced bulk density from 0.2 to 0.7 for pure hydrogen and hydrogen–carbon monoxide mixture are obtained. The theoretical calculations are in good agreement with the simulation results in this work and other data available in literature. The adsorption of hydrogen and the selectivity of hydrogen–carbon monoxide mixture are predicted from DFT and the adsorption characteristics of the isolated cylindrical wall is discussed.
- Published
- 2004
21. A modified fundamental measure theory for spherical particles in microchannels
- Author
-
Jianzhong Wu and Yang-Xin Yu
- Subjects
Sphere packing ,Classical mechanics ,Materials science ,Monte Carlo method ,General Physics and Astronomy ,SPHERES ,Density functional theory ,Hard spheres ,Physical and Theoretical Chemistry ,Molecular physics ,Liquid theory ,Freezing point - Abstract
Canonical-ensemble Monte Carlo simulation and an improved fundamental-measure theory are applied to calculating the structures and chemical potentials of neutral and associating spherical particles confined in rectangular or corrugated microchannels. It is found that the confinement significantly affects the distributions of neutral spheres in the microchannels, especially at high densities or near the confining surfaces. However, for associating particles, the combined effects of packing and association lead to virtually uniform density distributions. The density profiles calculated from the density functional theory agree well with simulation results for neutral hard spheres in both rectangular and corrugated microchannels except when the average packing density inside the channel is near the freezing point.
- Published
- 2003
22. Density functional study of hydrogen adsorption at low temperatures
- Author
-
Guang-Hua Gao, Yang-Xin Yu, and Chong Gu
- Subjects
Quantum fluid ,Hydrogen ,Monte Carlo method ,General Physics and Astronomy ,chemistry.chemical_element ,Thermodynamics ,symbols.namesake ,Adsorption ,chemistry ,Mean field theory ,Helmholtz free energy ,Quantum mechanics ,Path integral formulation ,symbols ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
In substitution of path integral isomorphism of the quantum particle, an effective polymer ring model is proposed in the density functional calculation for hydrogen adsorption in single-walled carbon nanotubes. The excess intrinsic Helmholtz energy for quantum particles includes contributions from hard-sphere repulsion, interatomic bonding and soft attraction. The first two contributions are considered through the method developed by Yu and Wu [J. Chem. Phys. 117, 2368 (2002)], and the last contribution is obtained from mean field approximation using Weeks–Chandler–Anderson potential. The theoretical predictions are in good agreement with Monte Carlo simulation data for the density distributions of the hydrogen molecule inside the tube. In addition, the proposed model is applied to the calculation of the adsorption isotherms of hydrogen at 100 and 150 K. The present model is simpler than the current existing theories for quantum fluids.
- Published
- 2003
23. Extended test-particle method for predicting the inter- and intramolecular correlation functions of polymeric fluids
- Author
-
Jianzhong Wu and Yang-Xin Yu
- Subjects
Correlation ,Distribution function ,Classical mechanics ,Chemistry ,Present method ,Intramolecular force ,Monte Carlo method ,General Physics and Astronomy ,Density functional theory ,Statistical physics ,Physical and Theoretical Chemistry ,Test particle ,Integral equation - Abstract
The Percus’ test-particle method is extended to predict the inter- and intramolecular correlation functions of polymeric fluids using a density functional theory developed earlier [J. Chem. Phys. 117, 2368 (2002)]. The calculated inter- and intramolecular distribution functions as well as the site–site correlation functions agree well with the results from Monte Carlo simulation for freely jointed hard-sphere chains. Compared with the integral-equation approaches and alternative density functional theories, the present method is free of molecular simulations as input and has the advantage of self-consistency among inter- and intramolecular correlation functions and thermodynamic properties.
- Published
- 2003
24. Structures of hard-sphere fluids from a modified fundamental-measure theory
- Author
-
Jianzhong Wu and Yang-Xin Yu
- Subjects
Physics ,Equation of state ,Orbital-free density functional theory ,General Physics and Astronomy ,Hard spheres ,Statistical mechanics ,symbols.namesake ,Helmholtz free energy ,symbols ,Development (differential geometry) ,Density functional theory ,Statistical physics ,Physical and Theoretical Chemistry ,Complex fluid - Abstract
We reformulate Rosenfeld’s fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state instead of that from the scaled-particle theory. The new density functional theory yields improved density distributions, especially the contact densities, of inhomogeneous hard-sphere fluids as well as more accurate direct and pair correlation functions of homogeneous hard spheres including those of highly asymmetric mixtures. This new density functional theory will provide an accurate reference for the further development of a statistical-thermodynamic theory of complex fluids at uniform and at inhomogeneous conditions.
- Published
- 2002
25. Density functional theory for inhomogeneous mixtures of polymeric fluids
- Author
-
Jianzhong Wu and Yang-Xin Yu
- Subjects
Adsorption ,Chain (algebraic topology) ,Solid-state physics ,Chemistry ,Monte Carlo method ,Excluded volume ,General Physics and Astronomy ,Thermodynamics ,Density functional theory ,Monotonic function ,Physical and Theoretical Chemistry ,Perturbation theory - Abstract
A new density functional theory is developed for inhomogeneous mixtures of polymeric fluids by combining Rosenfeld’s fundamental-measure theory for excluded volume effects with Wertheim’s first-order thermodynamic perturbation theory for chain connectivity. With no adjustable parameters, theoretical predictions are in excellent agreement with Monte Carlo simulation data for the density distributions and for the adsorption isotherms of hard-sphere chains near hard walls or in slit-like pores. This theory is applied to calculate the force between two parallel hard walls separated by hard-sphere chains at different densities. Calculated results indicate that the chain-mediated force is attractive and decays monotonically with separation at low chain densities, it oscillates at high chain densities and in between, it is attractive at small separation and repulsive at large separation. This new density functional theory is simpler than similar theories in the literature and is directly applicable to mixtures.
- Published
- 2002
26. DFT study on the atomic-scale nucleation path of graphene growth on the Cu(111) surface
- Author
-
Yang-Xin Yu, Meicheng Li, Fan Bai, Tai Wang, and Yingfeng Li
- Subjects
Surface (mathematics) ,Materials science ,Graphene ,Nucleation ,General Physics and Astronomy ,chemistry.chemical_element ,Copper ,Atomic units ,law.invention ,chemistry ,law ,Computational chemistry ,Chemical physics ,Path (graph theory) ,Density functional theory ,Physical and Theoretical Chemistry ,Carbon - Abstract
The nucleation path of graphene growth on the Cu(111) surface is investigated by importing carbon atoms step-by-step using density functional theory (DFT) calculations. An overall path of graphene nucleation has been proposed based on configuration and energy analysis. At the very first stage, linear chains will be formed and dominate the copper surface. Then, Y-type (furcate) carbon species will be shaped when new carbon atoms are absorbed aside the linear chains. Finally, ring-containing carbon species and graphene islands will be formed stepwise, with energetic preference. We find that the Y-type and ring-containing carbon species are not likely formed directly at the initial stage of graphene nucleation, but should be formed starting from linear chains. The nucleation limiting step is the formation of the Y-type species, which must pass an energy barrier of about 0.25 eV. These underlying observations are instructive to stimulate future experimental efforts on graphene synthesis.
- Published
- 2014
27. A density functional theory with a mean-field weight function: applications to surface tension, adsorption, and phase transition of a Lennard-Jones fluid in a slit-like pore
- Author
-
Bo Peng and Yang-Xin Yu
- Subjects
Phase transition ,Equation of state ,Chemistry ,Capillary action ,Thermodynamics ,Surfaces, Coatings and Films ,Surface tension ,symbols.namesake ,Mean field theory ,Helmholtz free energy ,Materials Chemistry ,symbols ,Density functional theory ,Physical and Theoretical Chemistry ,Complex fluid - Abstract
A new density functional theory (DFT) for an inhomogeneous 12-6 Lennard-Jones fluid is proposed based on the modified fundamental measure theory for repulsive interaction and a weighted density functional for attractive interaction. The Helmholtz free energy functional for the attractive part is constructed using the modified Benedict-Webb-Rubin equation of state with a mean-field weight function. Comparisons of the theoretical results with molecular simulation data suggest that the new DFT yields accurate bulk surface tension, density distributions, adsorption-desorption isotherms, pore pressures, and capillary phase transitions for the Lennard-Jones fluid confined in slitlike pores with different widths and solid-fluid interactions. The new DFT reproduces well the vapor-liquid critical temperatures of the confined Lennard-Jones fluid, whereas the mean-field theory always overestimates the critical temperatures. Because the new DFT is computationally as simple and efficient as the mean-field theory, it will provide a good reference for further development of a statistical-thermodynamic theory of complex fluid under both homogeneous and inhomogeneous conditions when disperse force has to be considered.
- Published
- 2008
28. A density functional theory for Lennard-Jones fluids in cylindrical pores and its applications to adsorption of nitrogen on MCM-41 materials
- Author
-
Yang-Xin Yu and Bo Peng
- Subjects
Equation of state ,Argon ,Chemistry ,Thermodynamics ,chemistry.chemical_element ,Surfaces and Interfaces ,Condensed Matter Physics ,Surface tension ,Pore water pressure ,Adsorption ,Electrochemistry ,General Materials Science ,Density functional theory ,Physics::Chemical Physics ,Mesoporous material ,Porous medium ,Spectroscopy - Abstract
A density functional theory (DFT) constructed from the modified fundamental-measure theory and the modified Benedict-Webb-Rubin equation of state is presented. The Helmholtz free energy functional due to attractive interaction is expressed as a functional of attractive weighted-density in which the weight function is a mean-field-like type. An obvious advantage of the present theory is that it reproduces accurate bulk properties such as chemical potential, bulk pressure, vapor-liquid interfacial tension, and so forth when compared with molecular simulations and experiments with the same set of molecular parameters. Capabilities of the present DFT are demonstrated by its applicability to adsorption of argon and nitrogen on, respectively, a model cylindrical pore and mesoporous MCM-41 materials. Comparison of the theoretical results of argon in the model cylindrical pore with those from the newly published molecular simulations indicates that the present DFT predicts accurate average densities in the pore, slightly overestimates the pore pressure, and correctly describes the effect of the fluid-pore wall interaction on average densities and pressures in the pore. Application to adsorption of nitrogen on MCM-41 at 77.4 K shows that the present DFT predicts density profiles and adsorption isotherms in good agreement with those from molecular simulations and experiments. In contrast, the hysteresis loop of adsorption calculated from the mean-field theory shifts toward the low pressure region because a low bulk saturated pressure is produced from the mean-field equation of state. The present DFT offers a good way to describe the adsorption isotherms of porous materials as a function of temperature and pressure.
- Published
- 2008
29. Density functional study on the structural and thermodynamic properties of aqueous DNA-electrolyte solution in the framework of cell model
- Author
-
Ke Wang, Yang-Xin Yu, and Guang-Hua Gao
- Subjects
Osmosis ,Static Electricity ,General Physics and Astronomy ,Thermodynamics ,Electrolyte ,Models, Biological ,Quantitative Biology::Cell Behavior ,symbols.namesake ,Electrolytes ,Phase (matter) ,Computer Simulation ,Statistical physics ,Poisson Distribution ,Physical and Theoretical Chemistry ,Donnan potential ,Chemistry ,Water ,DNA ,Electrostatics ,Boltzmann equation ,Solutions ,Helmholtz free energy ,symbols ,Quantum Theory ,Density functional theory ,Salts ,Poisson's equation - Abstract
A density functional theory (DFT) in the framework of cell model is proposed to calculate the structural and thermodynamic properties of aqueous DNA-electrolyte solution with finite DNA concentrations. The hard-sphere contribution to the excess Helmholtz energy functional is derived from the modified fundamental measure theory, and the electrostatic interaction is evaluated through a quadratic functional Taylor expansion around a uniform fluid. The electroneutrality in the cell leads to a variational equation with a constraint. Since the reference fluid is selected to be a bulk phase, the Lagrange multiplier proves to be the potential drop across the cell boundary (Donnan potential). The ion profiles and electrostatic potential profiles in the cell are calculated from the present DFT-cell model. Our DFT-cell model gives better prediction of ion profiles than the Poisson-Boltzmann (PB)- or modified PB-cell models when compared to the molecular simulation data. The effects of polyelectrolyte concentration, ion size, and added-salt concentration on the electrostatic potential difference between the DNA surface and the cell boundary are investigated. The expression of osmotic coefficient is derived from the general formula of grand potential. The osmotic coefficients predicted by the DFT are lower than the PB results and are closer to the simulation results and experimental data.
- Published
- 2008
30. Structures and correlation functions of multicomponent and polydisperse hard-sphere mixtures from a density functional theory
- Author
-
Guang-Hua Gao, Jianzhong Wu, Yang-Xin Yu, and Yuxuan Xin
- Subjects
Equation of state ,Distribution (mathematics) ,Chemistry ,Monte Carlo method ,General Physics and Astronomy ,Binary number ,Thermodynamics ,Density functional theory ,Statistical physics ,Statistical mechanics ,Physical and Theoretical Chemistry ,Uniform size ,Ternary operation - Abstract
The structures of nonuniform binary hard-sphere mixtures and the correlation functions of uniform ternary hard-sphere mixtures were studied using a modified fundamental-measure theory based on the weight functions of Rosenfeld [Rosenfeld, Phys. Rev. Lett. 63, 980 (1989)] and Boublik-Mansoori-Carnahan-Starling-Leland equation of state [Boublik, J. Chem. Phys. 53, 471 (1970); Mansoori et al., J. Chem. Phys. 54, 1523 (1971)]. The theoretical predictions agreed very well with the molecular simulations for the overall density profiles, the local compositions, and the radial distribution functions of uniform as well as inhomogeneous hard-sphere mixtures. The density functional theory was further extended to represent the structure of a polydisperse hard-sphere fluid near a hard wall. Excellent agreement was also achieved between theory and Monte Carlo simulations. The density functional theory predicted oscillatory size segregations near a hard wall for a polydisperse hard-sphere fluid of a uniform size distribution.
- Published
- 2004
31. Density functional study on the structures and thermodynamic properties of small ions around polyanionic DNA
- Author
-
Yang-Xin Yu, Guang-Hua Gao, and Ke Wang
- Subjects
Ions ,Models, Molecular ,Monte Carlo method ,Ionic bonding ,Thermodynamics ,Charge (physics) ,Integral equation ,Ion ,symbols.namesake ,Electrolytes ,Models, Chemical ,Helmholtz free energy ,Taylor series ,symbols ,Electrochemistry ,Nucleic Acid Conformation ,Density functional theory ,Computer Simulation ,Statistical physics ,Physics::Chemical Physics ,Mathematics - Abstract
A density functional theory (DFT) is presented for describing the distributions of small ions around an isolated infinitely long polyanionic DNA molecule in the framework of the restricted primitive model. The hard-sphere contribution to the excess Helmholtz energy functional is derived from the modified fundamental measure theory, and the electrostatic interaction is evaluated through a quadratic functional Taylor expansion. The predictions from the DFT are compared with integral equation theory (IET), the nonlinear Poisson-Boltzmann (PB) equation, and computer simulation data for the ionic density profiles, electrostatic potentials, and charge compensation functions at varieties of solution conditions. Good agreement between the DFT and computer simulations is achieved. The charge inversion phenomena of DNA are observed in a moderately concentrated solution of 2:1 and 2:2 electrolytes using the DFT, IET, and computer simulation, but can never be predicted from the PB equation. The predictions of charge inversion from the DFT prove to be more accurate than those from the IET when compared with computer simulation data. The preferential interaction coefficients from the DFT are also compared with those from the PB equation and Monte Carlo simulation, and it is shown that the DFT is superior to the PB equation.
- Published
- 2004
32. The over-step coalescence of carbon atoms on copper surface in the CVD growth of graphene: density functional calculations
- Author
-
Yue Yu, Yingfeng Li, Meicheng Li, Trevor Mwenya, Yang-Xin Yu, Fan Bai, and Gu Tiansheng
- Subjects
Coalescence (physics) ,Graphene ,General Physics and Astronomy ,chemistry.chemical_element ,Context (language use) ,Chemical vapor deposition ,Copper ,lcsh:QC1-999 ,law.invention ,Adsorption ,chemistry ,Chemical physics ,Computational chemistry ,law ,Physics::Atomic and Molecular Clusters ,Density functional theory ,Physics::Atomic Physics ,Carbon ,lcsh:Physics - Abstract
The ways in which carbon atoms coalesce over the steps on copper (111) surface are ascertained by density functional theory (DFT) calculations in the context of chemical vapor deposition (CVD) growth of graphene. Two strategies, (1) by putting carbon atoms on and under the steps separately and (2) by importing additional carbon atoms between the ones separated by the steps, have been attempted to investigate if an over-step coalescence of carbon atoms could take place. Based on analyses about the optimized configurations and adsorption energies of carbon atoms nearby the steps, as well as the energy evolution curve of the system throughout the geometry optimizations process, we determined the main way in which graphene grows over the steps continuously: the carbon atoms, adsorbed additionally on the locations between the already existing ones which are separated by the steps, link them (these carbon atoms separated by the steps) together. The direct over-step coalescence of the carbon atoms separated by the steps is very difficult, although the energy barrier preventing their coalescence can be weakened by importing carbon atoms on and under the steps gradually. Our results imply potential applications in directing the fabrication of graphene with particular structure by controlling the surface topography of copper substrate.
- Published
- 2013
33. Graphenylene: a promising anode material for lithium-ion batteries with high mobility and storage
- Author
-
Yang-Xin Yu
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Graphene ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,law.invention ,Anode ,Adsorption ,chemistry ,law ,Monolayer ,General Materials Science ,Density functional theory ,Lithium ,Carbon ,Lithium atom - Abstract
It is known that low-dimensional carbon allotropes can be used as a new class of anode materials for lithium-ion batteries. However, the existing carbon allotropes cannot meet the increasing energy and power demand, and thus there is still a need for further development of new materials for lithium-ion batteries. In the present work, a new graphene allotrope, known as graphenylene, is found to be capable of storing lithium with greater density of energy. Ab initio density functional theory calculations indicate that the unique dodecagonal holes in graphenylene enable lithium ions to diffuse both on and through graphenylene layers with energy barriers no higher than 0.99 eV. Adsorption of a lithium atom on graphenylene is stronger than that on pristine graphene. The highest lithium storage capacities for monolayer and bilayer graphenylene compounds are Li3C6 and Li2.5C6, respectively, which correspond to specific capacities of 1116 and 930 mA h g−1. Both specific and volumetric capacities of lithium-intercalated graphenylene compounds are significantly larger than those for graphene. The high lithium mobility and large lithium storage capacity demonstrate that graphenylene is a promising anode material for modern lithium-ion batteries.
- Published
- 2013
34. Ion distributions, exclusion coefficients, and separation factors of electrolytes in a charged cylindrical nanopore: A partially perturbative density functional theory study
- Author
-
Yang-Xin Yu and Bo Peng
- Subjects
chemistry.chemical_classification ,Physics::Biological Physics ,Quantitative Biology::Biomolecules ,Chemistry ,General Physics and Astronomy ,Charge density ,Electrolyte ,Boltzmann equation ,Ion ,Condensed Matter::Soft Condensed Matter ,Nanopore ,Chemical physics ,Density functional theory ,Statistical physics ,Physical and Theoretical Chemistry ,Poisson's equation ,Counterion - Abstract
The structural and thermodynamic properties for charge symmetric and asymmetric electrolytes as well as mixed electrolyte system inside a charged cylindrical nanopore are investigated using a partially perturbative density functional theory. The electrolytes are treated in the restricted primitive model and the internal surface of the cylindrical nanopore is considered to have a uniform charge density. The proposed theory is directly applicable to the arbitrary mixed electrolyte solution containing ions with the equal diameter and different valences. Large amount of simulation data for ion density distributions, separation factors, and exclusion coefficients are used to determine the range of validity of the partially perturbative density functional theory for monovalent and multivalent counterion systems. The proposed theory is found to be in good agreement with the simulations for both mono- and multivalent counterion systems. In contrast, the classical Poisson-Boltzmann equation only provides reasonable descriptions of monovalent counterion system at low bulk density, and is qualitatively and quantitatively wrong in the prediction for the multivalent counterion systems due to its neglect of the strong interionic correlations in these systems. The proposed density functional theory has also been applied to an electrolyte absorbed into a pore that is a model of the filter of a physiological calcium channel.
- Published
- 2009
35. A novel weighted density functional theory for adsorption, fluid-solid interfacial tension, and disjoining properties of simple liquid films on planar solid surfaces
- Author
-
Yang-Xin Yu
- Subjects
Argon ,Chemistry ,General Physics and Astronomy ,Thermodynamics ,chemistry.chemical_element ,Surface tension ,Neon ,Planar ,Adsorption ,Lennard-Jones potential ,Physical chemistry ,Density functional theory ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Porous medium - Abstract
A novel weighted density functional theory (WDFT) for an inhomogeneous 12-6 Lennard-Jones fluid is proposed based on the modified fundamental measure theory for repulsive contribution, the mean-field approximation for attractive contribution, and the first-order mean-spherical approximation with a weighted density for correlation contribution. Extensive comparisons of the theoretical results with molecular simulation and experimental data indicate that the new WDFT yields accurate density profiles, adsorption isotherms, fluid-solid interfacial tensions, as well as disjoining potentials and pressures of simple gases such as argon, nitrogen, methane, ethane, and neon confined in slitlike pores or near graphitic solid surfaces. The present WDFT performs better than the nonlocal density functional theory, which is frequently used in the study of adsorption on porous materials. Since the proposed theory possesses a good dimensional crossover and is able to correctly reduce to two-dimensional case, it performs very well even in very narrow pores. In addition, the present WDFT reproduces very well the supercritical fluid-solid interfacial tensions, whereas the theory of Sweatman underestimates them at high bulk densities. The present WDFT predicts that the increase in the fluid-wall attraction may change the sign of the interfacial tension and hence may make the wall from "phobic" to "philic" with respect to the fluid. The new WDFT is computationally as simple and efficient as the mean-field theory and avoids the second-order direct correlation function as an input. It provides a universal way to construct the excess Helmholtz free-energy functional for inhomogeneous fluids such as Yukawa, square-well, and Sutherland fluids.
- Published
- 2009
36. Preferential interaction between DNA and small ions in mixed-size counterion systems: Monte Carlo simulation and density functional study
- Author
-
Ke Wang, Yang-Xin Yu, Guangsheng Luo, and Guang-Hua Gao
- Subjects
Anions ,Models, Molecular ,Work (thermodynamics) ,Static Electricity ,Monte Carlo method ,General Physics and Astronomy ,Ionic bonding ,Thermodynamics ,Electrolyte ,Binding, Competitive ,Ion ,Electrolytes ,Computational chemistry ,Cations ,Computer Simulation ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Ions ,chemistry.chemical_classification ,Models, Statistical ,Chemistry, Physical ,DNA ,Models, Theoretical ,Boltzmann equation ,chemistry ,Nucleic Acid Conformation ,Density functional theory ,Counterion ,Monte Carlo Method - Abstract
Competitive binding between counterions around DNA molecule is characterized using the preferential interaction coefficient of individual ion in single and mixed electrolyte solutions. The canonical Monte Carlo (MC) simulation, nonlinear Poisson-Boltzmann (PB) equation, and density functional theory (DFT) proposed in our previous work [Wang, Yu, Gao, and Luo, J. Chem. Phys. 123, 234904 (2005)] are utilized to calculate the preferential interaction coefficients. The MC simulations and theoretical results show that for single electrolyte around DNA, the preferential interaction coefficient of electrolyte decreases as the cation size is increased, indicating that the larger cation has less accumulation ability in the vicinity of DNA. For the mixed electrolyte solution, it is found that cation diameter has a significant effect on the competitive ability while anion diameter has a negligible effect. It proves that the preferential interaction coefficients of all ions decrease as the total ionic concentration is increased. The DFT generally has better performance than the PB equation does when compared to the MC simulation data. The DFT behaves quite well for the real ionic solutions such as the KCl-NaCl-H2O, NaCl-CaCl2-H2O, and CaCl2-MgCl2-H2O systems.
- Published
- 2007
37. A density functional study of nitrogen adsorption in single-wall carbon nanotubes
- Author
-
Yao Wang, Jie Zhu, Wenjun Li, Fei Wei, and Yang-Xin Yu
- Subjects
Materials science ,Capillary condensation ,Mechanical Engineering ,chemistry.chemical_element ,Langmuir adsorption model ,Bioengineering ,Nanotechnology ,General Chemistry ,Carbon nanotube ,Nitrogen ,law.invention ,symbols.namesake ,Adsorption ,chemistry ,Chemical engineering ,Mechanics of Materials ,law ,Phase (matter) ,Monolayer ,symbols ,General Materials Science ,Density functional theory ,Electrical and Electronic Engineering - Abstract
An understanding of the adsorption behaviour of nitrogen in single-wall carbon nanotubes (SWCNTs) is necessary for obtaining information on its pores by nitrogen adsorption manometry. Non-local density functional theory was used to simulate nitrogen adsorption behaviour, including the adsorption isotherms, equilibrium density profiles and potential energy of the nitrogen molecules at 77 K, inside SWCNTs with diameters ranging from 0.696 to 3.001 nm. With increasing diameter, nitrogen adsorption changes from continuous filling in one dimension to a two-stage adsorption that corresponds to monolayer formation followed by multilayer condensation. The average density of the adsorbed nitrogen and the density profiles, especially in small diameter SWCNTs, were used to analyse the adsorbate phase at the saturation pressure. The results indicate that the type of pore filling depends primarily on the ratio of the SWCNT diameter to the adsorbate molecular diameter. The filling of SWCNTs is not a simple capillary condensation process, but is dominated by geometrical limitation.
- Published
- 2007
38. Density-functional theory and Monte Carlo simulation study on the electric double layer around DNA in mixed-size counterion systems
- Author
-
Ke Wang, Guang-Hua Gao, Yang-Xin Yu, and Guangsheng Luo
- Subjects
Anions ,Models, Molecular ,Materials science ,Cations, Divalent ,Quantum Monte Carlo ,Static Electricity ,Monte Carlo method ,General Physics and Astronomy ,Molecular physics ,Hybrid Monte Carlo ,Cations ,Electrochemistry ,Physics::Atomic and Molecular Clusters ,Kinetic Monte Carlo ,Statistical physics ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Ions ,chemistry.chemical_classification ,Models, Statistical ,DNA ,Models, Theoretical ,chemistry ,Research Design ,Dynamic Monte Carlo method ,Nucleic Acid Conformation ,Density functional theory ,Counterion ,Monte Carlo Method ,Algorithms ,Monte Carlo molecular modeling - Abstract
A density-functional approach and canonical Monte Carlo simulations are presented for describing the ionic microscopic structure around the DNA molecule immersed in mixed-size counterion solutions. In the density-functional approach, the hard-sphere contribution to the Helmholtz energy functional is obtained from the modified fundamental measure theory [Y.-X. Yu and J. Z. Wu, J. Chem. Phys. 117, 10156 (2002)], and the electrostatic contribution is evaluated through a quadratic functional Taylor expansion. The new theory is suitable to the systems containing ions of arbitrary sizes and valences. In the established canonical Monte Carlo simulation, an iterative self-consistent method is used to evaluate the long-range energy, and another iterative algorithm is adopted to obtain desired bulk ionic concentrations. The ion distributions from the density-functional theory (DFT) are in good agreement with those from the corresponding Monte Carlo (MC) simulations. It is found that the ratio of the bulk concentrations of two species of counterions (cations) makes significant contribution to the ion distributions in the vicinity of DNA. Comparisons with the electrostatic potential profiles from the MC simulations show that the accuracy of the DFT becomes low when a small divalent cation exists. Both the DFT and MC simulation results illustrate that the electrostatic potential at the surface of DNA increases as the anion diameter or the total cation concentration is increased and decreases as the diameter of one cation species is increased. The calculation of electrostatic potential using real ion diameters shows that the accuracy of DFT predictions for divalent ions is also acceptable.
- Published
- 2005
39. Structures and adsorption of binary hard-core Yukawa mixtures in a slitlike pore: Grand canonical Monte Carlo simulation and density-functional study
- Author
-
Fengqi You, Yang-Xin Yu, and Guang-Hua Gao
- Subjects
Chemistry ,Monte Carlo method ,Yukawa potential ,General Physics and Astronomy ,Thermodynamics ,Binary number ,Mole fraction ,symbols.namesake ,Grand canonical ensemble ,Gibbs isotherm ,Helmholtz free energy ,symbols ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
The grand canonical ensemble Monte Carlo simulation and density-functional theory are applied to calculate the structures, local mole fractions, and adsorption isotherms of binary hard-core Yukawa mixtures in a slitlike pore as well as the radial distribution functions of bulk mixtures. The excess Helmholtz energy functional is a combination of the modified fundamental measure theory of Yu and Wu [J. Chem. Phys. 117, 10156 (2002)] for the hard-core contribution and a corrected mean-field theory for the attractive contribution. A comparison of the theoretical results with the results from the Monte Carlo simulations shows that the corrected theory improves the density profiles of binary hard-core Yukawa mixtures in the vicinity of contact over the original mean-field theory. Both the present corrected theory and the simulations suggest that depletion and desorption occur at low temperature, and the local segregation can be observed in most cases. For binary mixtures in the hard slitlike pore, the present corrected theory predicts more accurate surface excesses than the original one does, while in the case of the attractive pore, no improvement is found in the prediction of a surface excess of the smaller molecule.
- Published
- 2005
40. Preparation and Properties of High‐Quality CexLayPryNd0.05Gd0.05B6 Single Crystal by Optical Float‐Zone Technique.
- Author
-
Ning, Shu‐Yu, Iitaka, Toshiaki, Xu, Dan‐dan, Li, Zhi, Wang, Yan, Yang, Xin‐Yu, and Zhang, Jiu‐Xing
- Subjects
DENSITY functional theory ,ELECTRON work function ,SINGLE crystals ,X-ray diffraction ,THERMAL electrons - Abstract
The work functions of LnB6 (Ln = Pr, Nd, and Gd) at (100) plane are systematically studied by first‐principles calculation based on density functional theory. It reveals that the work function of LnB6 at (100) plane obeys the relation of Φ(PrB6) < Φ(NdB6) < Φ(GdB6). The high‐quality CexLayPryNd0.05Gd0.05B6 (x = 0.5, y = 0.2 or x = 0.6, y = 0.15 or x = 0.7, y = 0.1) single crystals are successfully prepared by the optical float‐zone technique. The crystal quality and emission properties of single crystals are characterized by rotating target X‐ray diffraction, X‐ray single‐crystal diffraction, X‐ray Laue diffraction, and the thermal electron emission measurements. The results present that the as‐grown single crystals are of high quality and lower work function than single crystal CeB6. The maximum emission current density of 60.69 A cm−2 obtained at 1873 K under the applied voltage of 4000 V belongs to the Ce0.5La0.2Pr0.2Nd0.05Gd0.05B6 single crystal with (100) surface. The preparation, crystalline qualities, and thermionic emission properties of single crystal CexLayPryNd0.05Gd0.05B6 (x = 0.5, y = 0.2 or x = 0.6, y = 0.15 or x = 0.7, y = 0.1) are reported. The optimized emission properties of Jmax = 60.69 A cm−2 and Ф = 2.62 eV for Ce0.5La0.2Pr0.2Nd0.05Gd0.05B6 single crystal are superior over CeB6 single crystal. It is proved doping rare earth elements can reduce the work function and enhance the thermionic emission performance. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
41. Enhanced thermionic emission performance of LaB6 by Ce doping.
- Author
-
Ning, Shu-Yu, Iitaka, Toshiaki, Yang, Xin-Yu, Wang, Yan, Zhao, Jing-Jing, Li, Zhi, and Zhang, Jiu-Xing
- Subjects
- *
CESIUM , *THERMIONIC emission , *DOPING agents (Chemistry) , *DENSITY functional theory , *ELECTRON work function , *RARE earth metals - Abstract
Motivated by enhanced thermionic emission performance resulting from low work function, the work function of Ce x La 1− x B 6 is studied by first-principles calculation based on density functional theory. By calculation, the optimal Ce doping concentration is determined to be 0.25, and a very low work function Φ = 2.04 eV is predicted on the (001) surface of Ce 0.25 La 0.75 B 6 . High-quality Ce 0.25 La 0.75 B 6 single crystal was fabricated by optical floating zone technique. By the experimental measurement on the thermionic emission performance, the average work function of Ce 0.25 La 0.75 B 6 is about 2.61 eV, which is lower than the work function of both CeB 6 and LaB 6 . By the combination of calculation and experiment, we concluded that Ce doping can reduce the work function of LaB 6 and enhance its thermionic emission performance. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
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