Papers by Keyword: Density Functional Theory

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Authors: Jan S. Wróbel, Duc Nguyen-Manh, Krzysztof Jan Kurzydlowski
Abstract: In this chapter, we present the basic principles and methods for modelling of diffusion and phase stability of alloys using ab-initio methods. We review briefly first-principles methods and their most important approximations. The direct and approximated methods of prediction of migration energies are shown both for pure metals and for alloys. The cluster expansion method is described in more detail. We show that it can be applied to understand interactions in the alloys, to generate the representative structures of alloys and to predict migration barriers in alloys. We describe the methods to compute the effective cluster interactions and to assess the accuracy of the model. Finally, we present the examples of Monte Carlo simulations with parameters obtained from cluster expansion method. We show that the ordering in alloys can be predicted by the calculations of Warren-Cowley parameters. We investigate also the role of entropy in the stability of alloys at elevated temperatures.
Authors: Sergey N. Filimonov
Abstract: The absolute surface energies of three major low index surfaces of cubic silicon carbide (3C-SiC) are determined by first-principles density functional theory calculations. Calculations show that among clean 3C-SiC surfaces the Si-terminated 3C-SiC(001)-(3x2) surface has the lowest energy. The second and third lowest energy surfaces are the Si-terminated 3C-SiC(111)-(√3x√3) surface and the nonreconstructed 3C-SiC(110) surface. Hydrogen passivation greatly reduces both the absolute surface energies of the low index 3C-SiC surfaces and the surface energy anisotropy. In particular, the surface energies of fully passivated 3C-SiC(110) and (111) surfaces become indistinguishable at hydrogen-rich deposition conditions.
Authors: Abdullah Chik, S. Saad, Cheow Keat Yeoh, R.M. Zaki, F. Che Pa
Abstract: The electronic structure of the perovskite manganites AlMnO3 cubic crystal was presented. The calculations were made within density functional theory and PBE exchange correlations energy approximation. It was found that the crystal exhibit covalent bonding between Mn and O with superexchange mechanism. At groundstate, AlMnO3 stabilizes in antiferromagnetic structure with semi metallic like nature at the ground state.
Authors: A. Chik, S. Saad, R.M. Zaki, F. Che Pa, C.K. Yeoh
Abstract: The electronic structure of the perovskite manganites LaMnO3 and La2/3 Al1/3 MnO3 was presented. The calculations were made within density functional theory (DFT) and PBE exchange correlations energy approximation. It was found that inclusion of Al dopants add additional states near the Fermi level and decreasing the resistivity values for all temperature range.
Authors: Shubha Dubey, Gitanjali Pagare, Ekta Jain, Sankar P. Sanyal
Abstract: The structural properties and electronic properties of the intermetallic compound ErPb3 which crystallize in AuCu3 type structure (AB3) are studied by means of first principles total energy calculation using full potential linearized plane wave method (FP-LAPW) within the generalized gradient approximation of Perdew, Burke and Ernzrhof (PBE) and local spin density approximation (LSDA) for the exchange correlation functional and including spin magnetic calculation. The total energy is computed as a function of volume and fitted to the Birch-Murnaghan equation of state. The ground state properties of this compound such as equilibrium lattice parameter (a0), bulk modulus (B), and its pressure derivative (B’) are calculated and compared with the available experimental results. We find good agreement with the other theoretical and experimental results. For the compounds, the values of lattice constants obtained by PBE-GGA overestimates and by LSDA underestimates the available experimental values for the same, which verifies the reliability of the present calculation. The value obtained for the bulk modulus is 50.63 GPa. The analysis of electronic properties is achieved by the calculation of the band structures and the density of states in both the spin up and spin down modes, which show a metallic character of ErPB3 due to zero band gap. The values of calculated density of states are found to be 0.36 eV/states and 11.46 eV/states in spin-up and spin-down mode respectively. The calculated magnetic moment (μm) of ErPb3 is 2.06.
Authors: Veena Thakur, Gitanjali Pagare, Sankar P. Sanyal
Abstract: A theoretical study of structural and electronic properties of NdPd3 intermetallic compound has been investigated systematically using first principles density functional theory. The calculations are carried out within LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a0), bulk modulus (B) and its pressure derivative (B′) are calculated and obtained lattice parameter of this compound shows well agreement with the experimental results. From energy dispersion curves, it is found that the studied compound is metallic in nature.
Authors: Sajad Ahmad Dar, Vipul Shrivastav, Umesh Kumar Sakalle
Abstract: Intermetallic compounds are innovative materials and are far superior to conventional metals and alloys. These intermetallic compounds have a great potential in industrial and technological fields because most of the intermetallic compounds are stronger as well asstiffer at elevated temperature and provide far better corrosion resistance than conventional metals and alloys.Over the past few years the scientific interest in the study of these intermetallic compounds emanates greatly because of their high-tech applications. Our motivation of the present studyMgTl mainly consernedon the physical data generation in context with its possible vast applications .We used a theoretical approach within the local density approximation method to study the structural and electronic properties of MgTl by calculating total energy. As far as our calculations are concerned, the band structure shows the overlapping of conduction and valence band thus itis clear that MgTl in its pure form is a good conductor of heat and electricity and falls in the category of metals. We have also calculated lattice parameters, bulkmodules, first order derivative electronic and lattice heat coefficient and Debye temperature.
Authors: Hasani Chauke, Mordecai Mashamaite, Rosinah Modiba, Phuti Ngoepe
Abstract: In this study, we investigate the effect of ternary addition on the structural, mechanical properties and temperature dependence of Ti-based as potential shape memory alloys using molecular dynamics approach. We found that binary Ti-Pt alloys exhibit shape memory properties and display possible martensitic transformation from B2 to B19 phases. Partial addition with Zr, Co, Pd, Ir showed preferential ternary high temperature shape memory alloys formation of 6.25 at. % X composition (Ti-Pt-X). We found that the equilibrium lattice constants are in better agreement with the available experimental values. The heats of formation and elastic properties reveal possible composition and phases at temperature above 900 K with good shape memory properties. Their structures were confirmed using the X-ray diffraction patterns at different temperatures.
Authors: Nur Hafiz Hussin, Muhammad Noor Syazwan Saimin, Nunshaimah Salleh, Oskar Hasdinor Hassan, Muhd Zu Azhan Yahya, Mohamad Fariz Mohamad Taib
Abstract: In this study, first principles calculations based on density functional theory were used to evaluate optimized sructures and the total energy of the La doped PbTiO3 tetragonal (P4mm phase group). The calculations were conducted using local density approximation (LDA) functional as implemented in Cambridge Serial Total Energy Package (CASTEP) computer code. The different composition of Lanthanum (x) were doped on PbTiO3 resulting Pb1-xLaxTiO3 and its effect on the structural of Pb1-xLaxTiO3 were investigated. The different composition of La changed the lattice parameter and the volume of Pb1-xLaxTiO3. The total energy also were calculated and x= 0.2 is suitable composition of dapant to doped with PbTiO3 which is more stable compared with the other composition. The results are compared with experimental and other theoretical data.
Authors: Choon Min Cheong, Md Mahmudur Rahman, Abdul Halim Shaari, Soo Kien Chen
Abstract: In this work, we analyze the electronic structure and charge distribution of the YBCO family compounds Y-123 and Y-124 bulk using the density functional theory. The band structures and the density of states of the compounds are shown. The charge transfers between the atoms in the two compounds are compared and discussed in detail. The lattice parameters obtained by Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm are compared with the experimental parameters. The critical differences of the charge distribution for these two compounds are discussed.
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