arXiv subjects

Rajendra Prasad

Publications and source records attributed to Rajendra Prasad.

21 records · Page 2Linked to original sources

arXiv2007

Phase Stability in Ferroelectric Bismuth Titanate: A First Principles Study

Experimental data on the structure of ferroelectric oxide Bismuth Titanate suggests two different kinds of structures i.e. orthorhombic and monoclinic. We have performed density functional theory (DFT) based first principle calculations to determine the ground state structure of bismuth titanate, based on experimentally observed monoclinic and orthorhombic phases of Bi4Ti3O12. Both of these phases are optimized to zero pressure and lattice parameters were determined as a = 5.4370 Ang, b = 5.4260 Ang, c = 32.6833 Ang and Z = 4 for structure with space group B2cb and a = 5.4289 Ang, b = 5.4077 Ang, c = 32.8762 Ang, b = 90.08 deg and Z = 4 for the structure with space group B1a1 . Static and dynamic calculations show that the monoclinic structure with the space group B1a1 is the ground state structure. It is noted that small difference in the energies of both structures could be a factor behind experimental observation of either of the structure.

cond-mat.mtrl-sci↗

arXiv2007

The Exact Boundary Condition to Solve the Schrodinger Equation of Many Electron System

In an attempt to bypass the sign problem in quantum Monte Carlo simulation of electronic systems within the framework of fixed node approach, we derive the exclusion principle "Two electrons can't be at the same external isopotential surface simultaneously" using the first postulate of quantum mechanics. We propose the exact Coulomb-Exchange nodal surface i.e. the exact boundary condition to solve the non-relativistic Schrodinger equation for the non-degenerate ground state of atoms and molecules. This boundary condition was applied to compute the ground state energies of N, Ne, Li2, Be2, B2, C2, N2, O2, F2, and H2O systems using diffusion Monte Carlo method. The ground state energies thus obtained agree well with the exact estimate of non-relativistic energies.

cond-mat.str-el↗

arXiv2004

Metal-insulator transitions in tetrahedral semiconductors under lattice change

Although most insulators are expected to undergo insulator to metal transition on lattice compression, tetrahedral semiconductors Si, GaAs and InSb can become metallic on compression as well as by expansion. We focus on the transition by expansion which is rather peculiar; in all cases the direct gap at $Γ$ point closes on expansion and thereafter a zero-gap state persists over a wide range of lattice constant. The solids become metallic at an expansion of 13 % to 15 % when an electron fermi surface around L-point and a hole fermi surface at $Γ$-point develop. We provide an understanding of this behavior in terms of arguments based on symmetry and simple tight-binding considerations. We also report results on the critical behavior of conductivity in the metal phase and the static dielectric constant in the insulating phase and find common behaviour. We consider the possibility of excitonic phases and distortions which might intervene between insulating and metallic phases.

cond-mat.other↗