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Using density functional theory computations, the structures and electronic properties of hydrogenated and fluorinated aluminium nitride (AlN) were systematically investigated. We found that fully hydrogenated AlN (H–AlN–H) is an indirect-bandgap semiconductor which is similar to an AlN monolayer. Interestingly, Janus functionalized AlN (F–AlN–H) is a direct-bandgap semiconductor with a bandgap of 3.076 eV. F–AlN–H bilayer is also a direct-bandgap semiconductor, but its bandgap (only 0.187 eV) is much smaller than that of F–AlN–H monolayer. In addition, the gap values of both the F–AlN–H monolayer and the F–AlN–H bilayer can be continuously modulated by a perpendicular electric field; semiconductor–metal transition can even be obtained by applying a small electric field in the F–AlN–H bilayer. Our results are expected to shed light on the fabrication of electronic and optoelectronic devices based on AlN monolayer.

Van der Waals (vdW) heterostructure can improve the performance of the 2D materials and provide more applications. Based on density functional theory (DFT) calculations, the properties of vertical heterostructures formed by transition metal dichalcogenides (TMDs) MX2 (M = Mo, W; X = S, Se) and boron nitride (BP) were addressed. In particular, the vdW interaction exist in all these heterostructures instead of covalent bonding. The MoSe2/BP and WSe2/BP vdW heterostructures possess direct bandgap characterized by type-II band alignment and powerful built-in electric field across the interface, which can effectively separate the photogenerated-charge. Meanwhile, the MoS2/BP and WS2/BP vdW heterostructures also have the direct bandgap and intrinsic type-I band alignment. Furthermore, all heterostructures exhibit excellent optical absorption in the visible and near-infrared regions. Our investigation shows an effective method to design new vdW heterostructures based on TMDs and explores their applications for photocatalytic, photovoltaic, and optical devices.

Vacancy defects on an iron surface have a great influence on the occurrence of hydrogen embrittlement. The adsorption/dissociation mechanism of H2S and the diffusion behavior of H atoms were calculated by first-principles spin-polarization density functional theory (DFT) on defect-free and vacancy-defective Fe(1 0 0) surfaces. The results show that the maximum dissociation energy barriers of H2S on the Fe(1 0 0) surface of defect-free and first-layer vacancy-defective Fe are 0.35 and 0.17 eV, respectively, indicating that the reactivity of the vacancy-defective Fe(1 0 0) surface is moderately increased. The existence of vacancy defects changes the preferential H atom diffusion entrance to the subsurface and shortens the diffusion path. For H diffusion in bulk Fe(1 0 0), it is found that H atoms diffuse via a tortuous path from one tetrahedral-site to a neighboring tetrahedral-site rather than diffusing through a linear trajectory. Moreover, the previously suggested path via the octahedral site is excluded due to its higher barrier and the rank of the saddle point. Diffusion barriers computed for H atom penetration from the surface into the inner-layers are approximately 0.54 eV (except for second-layer vacancy defects), which are all greater than the activation energy for dissociation of H2S on the Fe(1 0 0) surfaces. This suggests that H diffusion is more probable than H2S dissociation as the rate-limiting step for hydrogen permeation into the bulk Fe(1 0 0).

Ceria-supported Pd single-atom catalysts (SACs) are important catalysts to catalyze the CO oxidation, often used in three-way catalysts to treat automobile exhaust gases. This paper uses density functional theory (DFT) calculations and transition state theory to systematically study the effect of Ga atom doping on the performance of the Pd/CeO 2 SACs system. Noticeably, the results of DFT calculations reveal that the stability of Pd single atoms supported on the surface of CeO 2 (111) was significantly augmented by doping Ga. An oxygen vacancy generated easily near the Ga and Pd site will act as a crucial role for activating the adsorbed oxygen molecule. Most importantly, the climbing image nudged elastic band (CINEB) calculations show that the doping of Ga remarkably reduces the highest energy barrier during the CO oxidation reaction, meaning that the catalytic performance of the CO oxidation reaction is promoted effectively. This work provides a new perspective for SACs modification.

The oligomerization of olefins is important to the production of the high hydrocarbons. In the oligomerization process, it is always accompanied by the reaction of hydrogenation. In the present article, we report that surface carbon affects the ethylene (C2H4) hydrogenation on the supported cobalt catalysts. Co/SiO2 catalyst is carburized with CO and Co3C structure as well as Co structure is revealed with Transmission Electron Microscopy (TEM). We investigate ethylene hydrogenation on the Co/SiO2 catalyst and the carburized Co3C-Co/SiO2 catalyst. It exhibits a high selectivity of C4 products on the carburized Co3C-Co/SiO2 catalyst. We further apply Density Functional Theory (DFT) calculation to study the effect of surface carbon on the dimerization of ethylene. Co(0001) and Co3C(2 2 1) are chosen to represent the Co/SiO2 and Co3C-Co/SiO2 catalysts, respectively. The dimerization of ethylene occurs by CCH3* species coupling instead of CH2CH2* coupling. The effective barrier of CCH3* coupling on Co(0001) is higher than that on Co3C(2 2 1). This explains the high selectivity to C4 products on the carburized Co3C-Co/SiO2 catalyst. Our study provides experimental and theoretical insight for the effect of surface carbon to the reaction of ethylene with hydrogen. It may guide us to reasonable design of the catalyst for olefin oligomerization.

The adsorption of sodium dimethyl dithiocarbamate (SDD) and butyl xanthate (BX) on sphalerite (1 1 0) surface in the absence and presence of water molecules was simulated using density functional theory (DFT). The results indicated that both the SDD and BX can chemically adsorb on the sphalerite surface in the absence of water molecules. However, the presence of water molecules on sphalerite surface significantly increases the adsorption energy of SDD and BX, which is detrimental to SDD and BX attachment on sphalerite surface. Particularly, the presence of water molecules changes the adsorption of BX on sphalerite surface from chemisorption to physical absorption, but the adsorption of SDD on sphalerite surface is still very strong like that of chemisorption. The results of DOS comparison analysis, electron density and Mulliken population analysis also confirmed the adsorption of SDD on sphalerite surface is more easy and stable than that of BX adsorption.

The emergence of transition metal dichalcogenides (TMD) as an exciting class of materials with appealing potentials in electronic and optoelectronics has drawn intensive attention in the past few years. Herein, we report the fabrication of NiSe2, which has been predicted to be a promising candidate in the field of electrocatalyst, by direct selenylation of the nickel substrate after epitaxial growth of selenium on a nickel foil. With a combination of photoelectron spectroscopy (PES), X-ray diffraction (XRD), scanning electron microscopy (SEM) and density function theory (DFT) calculations, it is possible to identify the phase transition among the previously reported stable Ni-Se phases and the ultimate formation of NiSe2 species by external annealing at varying temperatures. While SEM reveals the morphology of NiSe2 film with flat terraces, XRD, XPS and DFT calculations demonstrate that NiSe2 is the relatively stable phase formed on the Ni substrate from the cohesive energy point of view. Furthermore, valence band spectra point out the nonmetallic level of these different Ni-Se compounds, agreeing well with literature reports. In the end, our report may indicate a feasible approach to synthesize the pure NiSe2 species under solution-free condition and an encouraging step forward towards non-noble electrocatalysts.

We present a theoretical investigation of the reaction mechanism of TiCl4 dissociation on pyrolytic carbon surface and discuss the influence of H atom on adsorption and dissociation behaviors of TiCl4 by using density functional theory. The adsorption behaviors of TiClx (x = 4-0) and the interactions between pre-adsorbed H atom and TiClx are studied by calculating adsorption energies Eads and interaction energies HTi, respectively. The pre-adsorbed H atom significantly facilitates the adsorption of TiClx on pyrolytic carbon surface. Specially, TiCl3 adsorption on pyrolytic carbon surface converts from an endothermic process into an exothermic process due to the present of pre-adsorbed H atom. The calculation results of HTi show that the interactions between pre-adsorbed H atom and TiClx are attractive. The dissociation of TiCl4 on pre-adsorbed H pyrolytic carbon surface is an exothermic process, and TiCl4 → TiCl3 is the limited step. The dissociation barriers of each step are less than 1.5 eV except for TiCl → Ti, which does not need to overcome any barriers, that is to say, once TiCl is adsorbed on pre-adsorbed H surface the reaction of TiCl → Ti spontaneously occurs. It thus can be concluded that the dissociation of TiCl4 on pyrolytic carbon surface is a favorable process as long as H2 molecular have decomposed into atomic H and adsorbed on pyrolytic carbon surface, and the intermediate species (TiCl3, TiCl2 and TiCl) play an important role on the titanium CVD deposition. We also study the adsorption behavior of H atom and the dissociation behavior of H2 molecular on pyrolytic carbon surface.

To explore new sensor materials towards hazardous gases NH3, PH3, and AsH3, their adsorptions on pristine graphene and rare earth metal (REM = La, Ce, Nd, Pm, Sm, Eu and Gd) doped graphenes were studied by using density functional theory calculations. The adsorption energies show that pristine graphene exhibits weak physisorption towards the NH3, PH3, and AsH3 gas molecules. Almost no changes appear on the geometrical structures, charge populations and DOSs of pristine graphene. However, the rare earth metal element modifications lead to enhanced chemisorption towards NH3 and weakened adsorption towards AsH3, accompanied with significant electron redistribution and orbital hybridization. The electrical conductivity of the graphenic substrate is also increased, leading to higher sensor response towards NH3. Facile sensitivity and recovery time reveals Ce doped graphene is an ideal candidate for room temperature monitoring of NH3.

Intercalation has been experimentally proven to be an efficient approach for decoupling graphene from metal substrates such as Cu, which enables the easy transfer of graphene from a substrate. Thereby we propose a simple and effective method for injecting the H2S gas under an annealing environment to form sulfur compound intercalations, to help decouple graphene from the Cu substrate. Using density functional theory calculations, two different S-intercalating mechanisms, direct S intercalation and Hydrogen (H)-assisted S intercalation, have been found to occur at the zigzag and armchair edges of graphene, respectively. By forming various two-dimensional (2D) sulfide (Cu2S, CuS, and CuS2) intercalations depending on the temperature and S concentration, the electron interaction between the Cu substrate and graphene as well as the exfoliation energy of graphene from the Cu substrate can be effectively reduced. This allows graphene to decouple from the Cu substrate and become almost free-standing with a neutral charge under controlled experimental conditions. The stability of the sulfide intercalations has been proven by thermodynamic and kinetic simulations. H-assisted S intercalation may promote the subsequent transfer of graphene, enabling the practical application of large-sized graphene sheets grown by chemical vapor deposition on metal substrates.

Development of highly efficient, cost effective heteronuclear catalysts has been a huge interest in recent years due to its prime importance in environmental perpetuation. Among the developed catalysts, heteroatom-doped graphene catalysts for CO oxidation have attracted a global attention, due to its unique electronic properties suitable for CO oxidation. In this work, the oxidation mechanism of CO on various VIIIB dimeric metal-doped graphene with four atom vacancies systems (M1M2@C6) were investigated systematically by density functional theory (DFT) calculations. After a detailed analytic investigation through competition of adsorption performance and stability, FeFe@C6, FeCo@C6 and FeNi@C6 were found to be highly efficient and suitable as CO oxidation catalysts. Further, the heteronuclear dimeric catalysts (FeCo@C6 and FeNi@C6) were found to possess better catalytic activity over homonuclear dimeric catalyst (FeFe@C6) with much lower energy barrier for CO oxidation (0.79 eV, 0.49 eV, 0.42 eV for FeFe@C6, FeCo@C6, FeNi@C6). This investigation opens a new direction in designing the efficient and cost-effective graphene-based catalysts and also provides important hints for the understanding of catalytic reaction mechanisms for CO oxidation catalysis, which provides guidance and ideas for subsequent experimental synthesis of low-cost and efficient catalysts.

The density functional theory calculation has been conducted to investigate the structural and electronic properties, including the adsorption energies, bond structures, work functions, charge transfer behaviors, and density of states for pristine, Ni-, and Fe-embedded capped (5, 5) single-walled carbon nanotubes (SWNTs) with different coverage of atomic hydrogen, oxygen, and nitrogen adsorptions. Ni or Fe embedment enhances the adatom-SWNT interactions significantly for three kinds of gas atoms with the increases of the adsorption energies. The SWNT work function drops with H adsorption, while Ni or Fe embedment assists further the reduction. When increasing the coverage, the adsorption energy decreases and the work function climbs for O adsorption, but the nitrogen adsorption energy increases. The Bader charge transfer analysis implies that the cap possesses higher oxygen reduction activities than the tube, and the density of states analysis shows that Ni or Fe embedment deepens the C-adatom hybridizations.

Room temperature, low-cost and efficient single-atom catalysts for the CO oxidation was essential for the pollutant-free biological and ecological environment. Herein, the oxidation mechanism of CO on manganese (Mn) and nitrogen (N) co-doped single-vacancy graphene (MnN-SV) and double-vacancy graphene (MnN-DV) are studied through density functional theory (DFT) calculations. The MnN-SV have a more excellent catalytic performance for CO oxidation compared to MnN-DV due to the synergistic effect of the Mn and N atoms and the ligand effect. CO oxidation on MnN-SV results into two CO2 via the termolecular Eley–Rideal (TER) mechanism whose energy barrier of rate determining step (RDS) is 0.351 eV, indicating superior catalytic performance compared to the most known catalysts. In addition, MnN-SV catalyzes CO via the Langmuir-Hinshelwood (LH) mechanism with only an energy barrier of RDS is 0.727 eV, and the energy barrier for the second CO2 generated by Eley-Rideal (ER) mechanism is 0.691 eV. Technologically, present results provide a pathway for the development of an efficient and low-cost catalysts to oxidize CO at room temperature.

The morphology of BN seeds can be experimentally controlled and has a certain influence on the structural quality and nucleation efficiency of the surrounding graphene. By adopting the calculations using the density functional theory combine with transition state, we found that the sharp corners of normal triangular BN seed hinder the continuous C adsorption and aggregation around BN, and they can be etched by H2. Therefore, we theoretically investigated the process of etching triangular BN seeds with H2, along with the influence of BN seed morphology on the nucleation and growth of graphene on Cu substrates. The etching sequence of BN occurs from the corner N atom to the corner B atom, and the atoms at the side edge are inactive due to their higher adsorption energies and reaction barriers. After etching the BN seeds from a triangular to a hexagonal morphology, the graphene nucleation rates are up to ten times higher than those before etching and 105 times higher than those on a perfect Cu substrate. These results suggest the possibility of fabricating desirable BN edge structures and morphologies, and also provide a convenient way to improve the quality and growth rate of graphene on the Cu substrate.

Toxic gases destroy the ecological environment and endanger human health, which enlightened the researchers in development of new materials and technologies that effectively collect and capture toxic gases, and convert to harmless gases with the aid of catalyst. Density functional theory (DFT) calculations are performed to evaluate the changes in adsorption energy, charge transfer, sensitivity and Gibbs free energy for MnN4-decorated graphene (MnN4-Gra), graphene nanoribbons (MnN4-GNR), graphene nanosheets (MnN4-GNS), carbon nanotubes (MnN4-CNT) and C60 fullerenes (MnN4-C60) after adsorbing gas molecules, including NO, NO2, CO, SO2, NH3, H2S, N2O, O2, H2O and CO2. The most stable adsorption configuration of the molecule on MnN4-CS can be determined by molecular electrostatic potential and adsorption energy. The adsorption properties of MnN4-CS are mainly affected by doped atoms, curvature and size of the substrate. Among five tested materials, MnN4-C60 has good adsorption energy for toxic gases and is suitable for collecting and trapping gases. MnN4-Gra, MnN4-GNR and MnN4-GNS are evaluated as catalysts for oxygen reduction reaction (ORR), MnN4-Gra, MnN4-GNR, MnN4-CNT are suitable as catalysts for CO oxidation. Also the normal operating temperatures of gas sensors were determined by Gibbs free energy and molecular dynamics (MD). This investigation provides valuable information for designing high-performance gas sensors.

The structural and electronic properties of the capped (5, 5) single-walled carbon nanotube (SWNT), including the structural stability, the work function, and the charge transfer performance, are investigated for the substitutional nitrogen atom doping under different concentrations by first-principles density functional theory. The geometrical structure keeps almost intact with single or two N atom doping, while C N bonds may break up with serious defects for N concentrations of 23.3 at.% and above. The SWNT remains metallic and the work function drops after doping due to the upward shift of Fermi level, leading to the increase of the electrical conductivity. N doping enhances the oxygen reduction activity stronger than N adsorption because of higher charge transfers.

The adsorption and migration energies of a single carbon atom and the configuration evolution energies of two carbon atoms on a clean diamond (0 0 1) surface were calculated using the first principle method based on density functional theory to investigate the formation of ultra-nanocrystalline diamond (UNCD) film. The activation energy of a single atom diffusing along a dimer row is 1.96 eV, which is almost the same as that of a CH 2 migrating along a dimer row under hydrogen-rich conditions. However, the activation energy of a single atom diffusing along a dimer chain is 2.66 eV, which is approximately 1.55 times greater than that of a CH 2 migrating along a dimer chain in a hydrogen-rich environment. The configuration evolution of the two carbon atoms is almost impossible at common diamond film deposition temperatures (700–900 °C) because the activation energies reach 4.46 or 5.90 eV. Therefore, the high-energy barrier could result in insufficient migration of adatoms, leading to the formation of amorphous in UNCD films in hydrogen-poor CVD environment.

We present the calculations of the cubic perovskite KNbO 3 (0 0 1) surface with NbO 2 and KO terminations within the first-principles density functional theory. The electronic structure, surface energy, and charge distribution for both termination are calculated. For the case of NbO 2 -terminated surfaces, the largest atomic relaxation is in the first-layer atoms, while for KO terminations in the second-layer atoms. The surface energy for the KO terminated was 1.21 eV, higher than the calculated surface energy of 0.75 eV for NbO 2 termination, revealing that it takes much less energy to cleave on NbO 2 plane than on a KO plane. The band gaps for KO-terminated and NbO 2 -terminated surface are 1.70 and 1.30 eV, respectively. Mulliken population analysis shows the strong increase in the K O chemical bonding on the top surface of the KO-terminated slab and significant covalency for Nb O bonding.

The sensitivity of light metal functionalized boron carbide (BC3) sheets towards selected carbonaceous gases like CO, CO2, and CH4 is investigated by using first principles density functional theory calculations. We find that functionalization with alkali (Li, Na, K) and alkaline earth metals (Be, Mg, Ca), is a useful strategy to improve the sensitivity of graphene-like BC3 towards the mentioned gases. A semiconductor-to-metal transformation of BC3 is observed upon the introduction of metal dopants. Gas molecules are adsorbed on the metallized BC3 through weak chemisorption, which is an ideal scenario for gas sensing under practical working conditions. We find that the adsorption energies (Eads) of CO molecule are found to be 1.71, 0.48, 0.34, 0.35, 0.96, and 0.84 eV on Be-, Li-, Na-, K-, Mg-, and Ca-doped BC3, respectively. Similarly, CO2 binds to Li-, Be-, Mg-, and Ca- doped BC3 with Eads of 0.54, 0.87, 0.61, and 0.43 eV, respectively. For CH4, an Eads value of 0.74 eV turns out to be the strongest in case of Be-BC3. Bader charge analysis divulges that the transfer of charges results in the adsorption mechanism of the gases to the metallized BC3. In addition to feasible Eads, change in the work function upon the adsorption of gas molecules further confirms good sensitivity of the metallized BC3 towards CO, CO2 and CH4. Based on our findings, we deduce that metal-doped BC3 is an excellent candidate for the efficient sensing of harmful pollutants.

Al2MgC2 may form on the interface of SiC/Mg composite, and as substrate of heterogeneous nucleation, Al2MgC2 could refine α-Mg grain. So, interface system SiC/Al2MgC2/Mg is interesting to be further clarified, while the study about SiC/Al2MgC2 is still insufficient. In present work, interfacial bonding on SiC(1 1 1)/Al2MgC2(0 0 0 1) and role of carbon atoms are investigated by using density functional theory (DFT) method. Considering different interfacial termination and stacking sites, totally 18 models are examined. Si/C-terminated and top-site stacked model (denoted as Si/C_top) is identified as the most stable one. Interfacial fracture toughness is predicted as critical stress intensity factor K Ic int = 2.34∼2.99 MPa∙m1/2. Interfacial bonding mostly contributes from carbon atoms, which behave as charge acceptors, and charge transfer between interfacial C-Si atoms is confirmed. Peaks in PDOS of interfacial C atoms shift towards negative side. Especially for C atom in SiC(1 1 1), shift from −1.33 eV to less than −2.9 eV, which generates stronger interfacial bonding. For C atom in Al2MgC2(0 0 0 1), new peak forms around −8.08 eV, and mainly from C-2p2 orbital. Meanwhile, its s orbital peak negatively shifts from −9.71 eV to −11.61 eV. The interfacial Si-C covalent bonds are predominantly composed as hybridizations of C-2p2 and Si-3s2 around −8.1 eV, C-2p2 and Si-3s2 around −11.5 eV.

Surface properties play an important role in the application of antiperovskite Li3OCl as a promising solid-state electrolyte in all-solid-state Li-metal batteries. In this paper, we systematically investigated the stability, geometric structure, electronic properties and Li-ion mobility of a Li3OCl (1 0 0) surface using first-principles density functional theory calculations. Several geometric structure models were considered with different low Miller indices to obtain the most stable surface structure. The surface energies revealed that the Li3OCl (1 0 0) surface with Li- and Cl-termination on both sides was the most stable configuration, and the stability of the configuration was further verified by calculating the atomic relaxation and electronic properties. In addition, four types of point defects in the Li3OCl (1 0 0) surface were considered to study the Li-ion mobilities on the surface, and the results from calculating the defect formation energies and migration energy barriers showed that interstitial Li with a migration energy barrier of 0.086 eV is the most important carrier at the surface. The results provide fundamental insights into Li3OCl surface properties and Li-ion mobility at the surface.

The structural, adhesive, and electronic properties of α-W(1 1 0)/α-WC(0 0 0 1) interfaces are studied by first-principles calculation based on density functional theory (DFT). Six different W/WC interface geometries are considered in this study, including two terminations of WC(0 0 0 1) surface, and each of them involves three different stacking sequences. It is demonstrated that whatever stacking sequence is, the interfacial separations of C-terminated interfaces decrease after optimization, and the lateral movement of the interfacial W atoms will bring three nearest neighbor C atoms around it. Therefore, the C-terminated interfaces are stable geometries, and yield larger adhesion energy, Wad. Using several analytic techniques including charge density distribution and its difference, and density of states, we characterized the electronic properties and determined the interfacial bonding of W-terminated hollow-site interface to be of metallic nature while the interfacial bonding of C-terminated hollow-site interface to be of a mixed covalent–ionic nature.

a b s t r a c t Formation of oxygen vacancies by introducing various mixed-valent cation dopants is a common practice to improve the cathode performance in solid oxide fuel cells. A computational procedure is developed in this work to predict the equilibrium oxygen vacancy non-stoichiometric concentrations at experimen- tally relevant temperatures and oxygen partial pressures for both bulk and surface oxide phases. The calculations are based on the first-principles density functional theory and a constrained free-energy functional. Quantitative agreements are found by direct comparisons to the thermogravimetry and solid electrolyte coulometry measurements for the strontium-doped lanthanum cobalt iron oxides at different compositions. Our results indicate that the oxygen vacancies are energetically stabilized at surfaces for all temperatures and all oxygen partial pressures, while such surface stabilization effects become stronger at higher temperatures and lower oxygen partial pressures.

s Understanding the interaction mechanisms of hydrogen sulfide (H 2 S) with graphene is important in developing graphene-based sensors for gas detection and removal. In this study, the effects of doped Fe atom on interaction of H 2 S with graphene were investigated by density functional theory calculations. Analyses of adsorption energy, electron density difference, and density of states indicated that the doped Fe atom can significantly improve the interaction of H 2 S gas molecules with graphene, as well as Pt-doped graphene. The location of the sulfur atom is important in the interactions between H 2 S and Fe-doped graphene. The influence of the Fe S distance can be very weak within a certain distance, as simulated in this study.

The β-SiC(1 1 1)/α-W(1 1 0) interfaces were studied by first-principles calculations based on density functional theory (DFT). The ideal work of adhesion (Wad) and interface energy (γint) were calculated for six different interfacial structures, taking into account both Si- and C-terminations of β-SiC(1 1 1) surfaces, and three different stacking sequences. The interfacial electronic structures including charge density distribution and difference, and density of states (DOS) were simulated to determine the nature of SiC/W bonding. The results show that the Si-terminated top-site interface is the most stable interface, yielding the highest Wad and the lowest γint. During the optimization, the Si-terminated top-site interface will transform into the center-site structure, resulting in the interaction among the interfacial W and Si atoms, and subinterfacial C atoms. In addition, the calculated interface energies show that an interdiffusion layer will form on the SiC/W interface. The experimental results also have verified the existence of an interdiffusion layer on the SiC/W interface in a CVD-SiC fiber.

The adsorption of CO molecule on the LaCoO 3 (0 0 1) surface has been investigated using density functional theory calculation. Calculation results show that the most suitable configuration is Co CO structure for the CoO-terminated LaCoO 3 (0 0 1) surface. In the adsorption process electrons transfer from CO molecule to the surface. The Co C bond is mainly from the hybrid between the CO and Co-d orbital. When CO molecule adsorption on the LaO-terminated LaCoO 3 (0 0 1) surface, the most suitable configuration is the O CO structure and the electrons transfer from the surface to the CO molecule in the adsorption process. The bond between the C atom and the surface O atom is mainly from the hybrid between the C-2p and O-2p orbital. The LaCoO 3 could be used as the gas sensing material to detect CO gas.

We performed first-principles density functional theory calculation to investigate the electronic structures and magnetic properties of Fe/NO 2 co-doped graphene. First, our study shows that the Fe/NO 2 co-doped graphene preserves the unique linear dispersion of the charge carriers. More importantly, NO 2 co-doping is a much effective way to compensate the shifting of E F , which can facilitate the Fe adsorbed graphene systems to retain the unique properties of graphene. Second, magnetic exchange energy calculation finds that long-range ferromagnetic coupling exists between two n-p pairs and the coupling strength can be obviously improved after NO 2 co-doping.

Understanding the interaction mechanisms of CO, NO, SO2, and HCHO with graphene are important in developing graphene-based sensors for gas detection and removal. In this study, the effects of doped Ti or N atom on the interaction of these gases with graphene were investigated by density functional theory calculations. Analyses of adsorption energy, electron density difference, and density of states indicated that the doped Ti atom could greatly improve the interaction of gas molecules with graphene. The Ti-doped graphene sheet demonstrated selective gas absorption. The order of interaction between the gas molecules and the Ti-doped graphene sheet was as follows: SO2 > NO > HCHO > CO. By contrast, the N-doped graphene sheet did not exhibit apparent selective gas absorption. These results imply that the Ti-doped graphene sheet is more effective than the N-doped graphene sheet in detecting and removing gas molecules because of its high selectivity.

Electronic structure modeling is carried out for bulk Pd–H system with implications for certain surface effects and hydrogen transport. The calculation is performed under the framework of density functional theory. The results provide new insight into the charge state of H inside Pd. The H is slightly negatively charged over the composition range studied, and the negative charge around the proton increases with an increasing loading of hydrogen. By studying the behavior of H at the “bridging” site, which is important to surface and transport phenomena, this paper helps to explain why the effective charge observed in H drift experiments is different from the static charge state.

In this study, we present the adsorption behavior of NO, NO2 and H2O on trivalent rare-earth ion-exchanged ZSM-5 (RE-ZSM-5; RE=La, Ce, Nd, Sm, Gd and Dy) using density functional theory. The results show that Ce-ZSM-5 is more effective for the activation of NOx than La-ZSM-5 and Nd-ZSM-5, which is in good agreement with experimental results. The present investigation also suggests that Dy-ZSM-5 has a considerable ability for the activation of NO2 as compared to Sm-ZSM-5 and Gd-ZSM-5. Furthermore, the Ce-, Nd- and Dy-analogues posses a quite stronger affinity for NOx and that the low affinity of H2O indicate the poisoning resistance ability of these catalysts. In addition, the relationship between the adsorption energy of NO and the contribution of NO-2πg1 molecular orbital was also investigated in the NO/RE-ZSM-5 adsorption complex.