Papers by Keyword: Pseudopotential Method

Abstract: The pseudopotential method and density functional theory with Hubbard correction were used to study changes in the atomic and electronic structure of yttrium orthoferrite (YFeO₃) during vacancy formation. Depending on the value of non-stoichiometry in YFeO_3−δ (δ = 0.0625 and 0.25), the energy gain of one of the two types of vacancy decreases from 0.3 to 0.1 eV. So it have been shown that high concentrations of oxygen vacancies make more insignificant the difference in the type of formed vacancies.

Abstract: In the present study, we have computed the electronic band structure and electronic charge density of the alloy (Be, Cd)Se in the zinc-blende structure; using the local Empirical Pseudopotential Method (EPM), which takes into account the disorder effect into the Virtual Crystal Approximation (VCA) by introducing an effective potential disorder. The obtained results show a reasonable agreement with the available experimental data. Detailed plots of the valence charge distribution along the [111] direction and in the (110) plane are also presented and discussed.

Abstract: In the present work, we have investigated total energy, bulk modulus, elastic constants, pressure derivatives of elastic constants and pressure derivative of bulk modulus of HgX (X=S, Se and Te) semiconducting compounds using higher-order perturbation scheme with the application of our own proposed model potential. To consider exchange and correlation effect to the dielectric function, the local-field correction function proposed by Farid et al is employed in the present study. In most of the cases the experimental and other theoretical results of the aforesaid physical properties of the HgX are not available in the literature and hence this study provides a better set of theoretical results of the physical properties of the materials for future comparison either with theoretical or experimental results.

Abstract: Neutral PBDEs congeners and their corresponding radical anions were studied with the pseudopotential method of stuttgart group (SDD) effective-core potentials basis set for the bromine atoms and the all-electron basis set for all other atoms. The pseudopotential method can be used for compounds containing heavy elements with relativistic effects and can reduce the computational time. The quantitative structure property relationship (QSPR) study was also performed in this work to develop models to predict the normolized reaction rate constants for the reductive debromination of polybrominated diphenyl ethers (PBDEs) by zero-valent iron (ZVI). The partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for the QSPR study between the molecular descriptors and the logarithm of normalized reaction rate constants of fourteen selected BDE congeners. The results show that the ANN models could be more satisfactorily to predict the rate constants than the PLSR and PCA-MLR models.

Abstract: In the present investigation, we report theoretical study of total energy, energy band gap in X-direction, bulk modulus, elastic constants and pressure derivative of elastic constants of Si_1-xSn_xsolid solution using higher-order perturbation theory along with application of our proposed potential, where x is concentration of Sn. The parameter of our potential is determined using zero-pressure equilibrium condition. In the present calculations, The local-field correction function can be employed to consider exchange and correlation effects. The present study showed that the physical quantities under investigation varied with the concentration of the constituent element.

Abstract: Pt nano-particles are supported on carbon materials at the electrode catalysts of protonexchange menbrane fuel cells. Pt nano-particles are desirable to be strongly adsorbed on carbon materials for high dispersion, although strong Pt-C interactions may affect the catalytic activity of small clusters. Thus we have examined H-atom absorption on Pt clusters supported or unsupported on graphene sheets, using first-principles calculations. For Pt-atom/graphene systems, a H atom is more weakly adsorbed than for a free Pt atom, and the H-Pt interaction becomes weaker if the interaction between a Pt atom and graphene becomes stronger. For the Ptn-cluster/graphene systems (n=2-4), the H-Pt interactions are also substantially changed from those for free Pt clusters. In the Pt clusters on graphene, the Pt-Pt distances are substantially changed associated with the electronicstructure changes by the Pt-C interactions. These structural and electronic changes in the Pt clusters as well as the presence of graphene itself seem to cause the changes in the absorption energies and preferential sites of H-atom absorption.

Abstract: Formation energies of various defects in Al₂O₃ and SiO₂ are calculated by using the plane-wave pseudopotential method. Also, the formation energies of Schottky defects and Frenkel defects are evaluated on the basis of these calculations. It is shown that formation energies of these defects are higher in SiO₂ than in Al₂O₃. In other words, less defects are formed in SiO₂ than in Al₂O₃. It is also found that the principal defect is the cation Frenkel defect in Al₂O₃ but the anion Frenkel defect in SiO₂. These results agree with the experimental results that Al ions diffuse preferably in Al₂O₃ but oxygen ions diffuse in SiO₂ at high temperatures.