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By using DFT simulations employing the GGA/PBE and LDA/CA-PZ approximations, the effects of the Hubbard U correction on the crystal structure, electronic properties, and chemical bands of the cubic phase ( P m3¯m) of STO were investigated. Our findings showed that the cubic phase ( P m3¯m) STO's band gaps and lattice parameters/volume are in reasonably good accordance with the experimental data, supporting the accuracy of our model. By applying the DFT + U method, we were able to obtain band gaps that were in reasonably good agreement with the most widely used experimental band gaps of the cubic ( P m3¯m) phase of STO, which are 3.20 eV, 3.24 eV, and 3.25 eV. This proves that the Hubbard U correction can overcome the underestimation of the band gaps induced by both GGA/PBE and LDA/CA-PZ approximations. On the other hand, the Sr-O and Ti-O bindings appear predominantly ionic and covalent, respectively, based on the effective valence charges, electron density distribution, and partial density of states analyses. In an attempt to enhance the performance of STO for new applications, these results might also be utilized as theoretical guidance, benefitting from our precise predicted values of the gap energies of the cubic phase ( P m3¯m).

We performed B3PW and B3LYP computations for BaTiO 3 (BTO), CaTiO 3 (CTO), PbTiO 3 (PTO), SrTiO 3 (STO), BaZrO 3 (BZO), CaZrO 3 (CZO), PbZrO 3 (PZO) and SrZrO 3 (SZO) perovskite neutral (001) along with polar (011) as well as (111) surfaces. For the neutral AO- as well as BO 2 -terminated (001) surfaces, in most cases, all upper-layer atoms relax inwards, although the second-layer atoms shift outwards. On the (001) BO 2 -terminated surface, the second-layer metal atoms, as a rule, exhibit larger atomic relaxations than the second-layer O atoms. For most ABO 3 perovskites, the (001) surface rumpling s is bigger for the AO- than BO 2 -terminated surfaces. In contrast, the surface energies, for both (001) terminations, are practically identical. Conversely, different (011) surface terminations exhibit quite different surface energies for the O-terminated, A-terminated and BO-terminated surfaces. Our computed ABO 3 perovskite (111) surface energies are always significantly larger than the neutral (001) as well as polar (011) surface energies. Our computed ABO 3 perovskite bulk B-O chemical bond covalency increases near their neutral (001) and especially polar (011) surfaces.

The rational construction of photocatalysts possesses tremendous potential to solve the energy crisis and environmental pollution; however, designing a catalyst for solar-driven overall water-splitting remains a great challenge. Herein, we propose a new MoS 2 -based photocatalyst (Co-P@MoS 2 ), which skillfully uses the cobalt (Co) atom to stimulate in-plane S atoms and employs the phosphorus (P) atom to stabilize the basal plane by forming the Co-P bands. Using density functional theory (DFT), it was found that oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) can occur at the P site and S2 site of the Co-P@MoS 2 , respectively, and the dual-active sites successfully makes a delicate balance between the adsorption and dissociation of hydrogen. Furthermore, the improved overall water-splitting performance of Co-P@MoS 2 was verified by analyzing the results of the electron structure and the dynamics of photogenerated carries. It was found that the imbalance of electron transfer caused by the introduction of the Co atom was the main contributor to the catalytic activity of Co-P@MoS 2 . Our study broadens the idea of developing photocatalysts for the overall water-splitting.

We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic ( P m3¯m) and tetragonal ( P 4mm) phases of PbTiO 3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO 3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO 3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti-O and Pb-O bonds. In addition, the study of the optical properties of the two phases of PbTiO 3 , by applying Hubbard' U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline that the GGA/PBE approximation with the Hubbard U potential correction could be an effective method for obtaining reliable band gap predictions with moderate computational cost. Therefore, these findings will enable theorists to make use of the precise values of these two phases' gap energies to enhance PbTiO 3 's performance for new applications.

The fabrication of type II heterojunctions is an efficient strategy to facilitate charge separation in photocatalysis. Here, mixed dimensional 0D/2D van der Waals (vdW) heterostructures (graphene quantum dots (GQDs)-MoS 2 ) for generating hydrogen from water splitting are investigated based on density functional theory (DFT). The electronic and photocatalytic properties of three heterostructures, namely, C 6 H 6 -MoS 2 , C 24 H 12 -MoS 2 and C 32 H 14 -MoS 2 are estimated by analyzing the density of states, charge density difference, work function, Bader charge, absorption spectra and band alignment. The results indicated that the built-in electric fields from GQDs to MoS 2 boost charge separation. Meanwhile, all the GQDs-MoS 2 exhibit strong absorption in the visible light region. Surprisingly, the transition of heterojunctions from type I to type II is realized by tuning the size of GQDs. In particular, C 32 H 14 -MoS 2 with enhanced visible-light absorption and an appropriate band edge position, as a type II heterostructure, may be a promising photocatalyst for generating hydrogen from water splitting. Thus, in this work a novel type II 0D/2D nanocomposite as a photocatalyst is constructed that provides a strategy to regulate the type of heterostructure from the perspective of theoretical calculation.

The atomic structure of antiphase boundaries in Sr-doped lanthanum scandate (La 1- x Sr x ScO 3- δ ) perovskite, promising as the proton conductor, was modelled by means of DFT method. Two structural types of interfaces formed by structural octahedral coupling were constructed: edge- and face-shared. The energetic stability of these two interfaces was investigated. The mechanisms of oxygen vacancy formation and migration in both types of interfaces were modelled. It was shown that both interfaces are structurally stable and facilitate oxygen ionic migration. Oxygen vacancy formation energy in interfaces is lower than that in the regular structure, which favours the oxygen vacancy segregation within such interfaces. The calculated energy profile suggests that both types of interfaces are advantageous for oxygen ion migration in the material.

On the basis of time-dependent density functional theory (TD-DFT) we performed first-principle calculations to predict optical properties and transition states of pristine, N- and S-doped, and N+S-codoped anatase TiO2 nanotubes of 1 nm-diameter. The host O atoms of the pristine TiO2 nanotube were substituted by N and S atoms to evaluate the influence of dopants on the photocatalytic properties of hollow titania nanostructures. The charge transition mechanism promoted by dopants positioned in the nanotube wall clearly demonstrates the constructive and destructive contributions to photoabsorption by means of calculated transition contribution maps. Based on the results of our calculations, we predict an increased visible-light-driven photoresponse in N- and S-doped and the N+S-codoped TiO2 nanotubes, enhancing the efficiency of hydrogen production in water-splitting applications.

A structurally stable stacked multilayer carbonitride is predicted with the aid of ab initio calculations. This carbonitride consists of C3N tetrahedra, and is similar to T-carbon and thus named T-C3N. Its 2-dimensional (2D) monolayer is also carefully investigated in this work. The studies on electronic properties reveal that bulk and 2D T-C3N are insulators with a 5.542 eV indirect band gap and a 5.741 eV direct band gap, respectively. However, the monolayer T-C3N exhibits an excellent uniform porosity. Its 5.50 Å pore size is perfect for water nanofiltration. The adsorption and permeation of water molecules on the monolayer T-C3N are investigated. Its promising potential application in highly efficient nanofiltration membranes for seawater desalination is discussed.

Karrikins (KARs) are a class of smoke-derived seed germination stimulants with great significance in both agriculture and plant biology. By means of direct binding to the receptor protein KAI2, the compounds can initiate the KAR signal transduction pathway, hence triggering germination of the dormant seeds in the soil. In the research, several molecular dynamics (MD) simulation techniques were properly integrated to investigate the binding process of KAR 1 to KAI2 and reveal the details of the whole binding event. The calculated binding free energy, -7.00 kcal/mol, is in good agreement with the experimental measurement, -6.83 kcal/mol. The obtained PMF profile indicates the existence of three intermediate states in the binding process. The analysis of the simulation trajectories demonstrates that, in the intermediate structures, KAR 1 is stabilized by some hydrophobic residues (Phe26, Phe134, Leu142, Trp153, Phe157, Leu160, Phe194), along with several bridging water molecules, and meanwhile, the significant shifting occurs in the local conformation of the protein as the ligand's binding. A series of the residues (Gln141-Phe157) on the so-called "cap domain" are proposed to be responsible for capturing the ligand at the initial stage of the binding. Besides, the changes of the ligand's poses are also quantitatively characterized by the proper choice of the coordinate system. Our work will contribute to the more penetrating understanding of the ligand binding process and the receptor affinity difference between several members in the KAR family and help design new, more effective germination stimulants.

We present the results of calculations of surface relaxations, rumplings, energetics, optical band gaps, and charge distribution for the SrZrO(3) and PbZrO(3) (001) and (011) surfaces using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. We consider both SrO(PbO) and ZrO(2) terminations of the (001) surface and Sr(Pb), ZrO, and O terminations of the polar SrZrO(3) and PbZrO(3) (011) surfaces. On the (001) surfaces, we find that all upper and third layer atoms relax inward, while outward relaxations of all atoms in the second layer are found with the sole exception of the SrO-terminated SrZrO(3) (001) surface second layer O atom. Between all (001) and (011) surfaces the largest relaxations, more than 15% of the bulk lattice constant, are for the Sr- and Pb-terminated SrZrO(3) and PbZrO(3) (011) surface upper layer Sr and Pb atoms. Our calculated surface rumpling for the SrO- and PbO-terminated SrZrO(3) and PbZrO(3) (001) surfaces (6.77 and 3.32% of a(0)) are by a factor of ten larger than the surface rumpling for the ZrO(2)-terminated (001) surfaces (-0.72 and 0.38% of a(0), respectively). In contrast to the surface rumpling, the (001) surface energies are comparable and in the energy range from 0.93 eV/cell for the ZrO(2)-terminated PbZrO(3) surface to 1.24 eV/cell for the ZrO(2)-terminated SrZrO(3) surface. In contrast to the (001) surface, different terminations of the SrZrO(3) and PbZrO(3) (011) surfaces lead to very different surface energies ranging from 1.74 eV/cell for the Pb-terminated PbZrO(3) (011) surface to 3.61 eV/cell for the ZrO-terminated SrZrO(3) (011) surface. All our calculated (011) surface energies are considerably larger than the (001) surface energies. Our calculated optical band gap for the SrZrO(3) bulk, 5.31 eV, is in fair agreement with the experimental value of 5.6 eV. All our calculated optical band gaps for the SrZrO(3) and PbZrO(3) (001) and (011) surfaces are reduced with respect to the bulk. We predict a considerable increase in the Zr-O chemical bond covalency near the SrZrO(3) and PbZrO(3) (011) surfaces as compared both to the bulk and to the (001) surface., (© 2010 IOP Publishing Ltd)

The ground state of H-center systems for the SrF(2) crystal is simulated with two different arrangements, which are oriented along either [100] or [111] axes. The calculations are based on hybrid Hartree-Fock and density functional theory exchange functionals by using Becke's three-parameter method combined with the nonlocal correlation functionals of Perdew and Wang. The energy difference between H centers with different orientations shows that the H center oriented in the [111] direction in alkaline earth fluorides is the most stable configuration. The geometric relaxations of the neighboring atoms surrounding the H centers are presented. The combination energy of an H center and the formation energy of the related F-H pair in both alkaline earth fluorides are discussed. We report also the electronic structure of the H center systems. The effective charges and spins of the substitutional and interstitial fluorine atoms show that the hole is located at the interstitial fluorine in the system with the [111] orientation of the H center. The band structures are illustrated. With the help of studying the total and partial density of states, the constituents of the defect bands are clarified.

Combining B3PW hybrid exchange-correlation functional within the density functional theory (DFT) and a supercell model, we calculated from the first principles the electronic structure of both ideal PbZrO(3) (001) surface (with ZrO(2)- and PbO-terminations) and a neutral oxygen vacancy also called the F center. The atomic relaxation and electronic density redistributions are discussed. Thermodynamic analysis of pure surfaces indicates that ZrO(2) termination is energetically more favorable than PbO-termination. The O vacancy on the ZrO(2)-surface attracts approximately 0.3 e (0.7 e in the bulk PbZrO(3)), while the remaining electron density from the missing O(2-) ion is localized mostly on atoms nearest to a vacancy. The calculated defect formation energy is smaller than in the bulk which should lead to the vacancy segregation to the surface. Unlike Ti-based perovskites, the vacancy-induced (deep) energy level lies in PbZrO(3) in the middle of the band gap.