Sanjay D. Gupta

Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3

A first principles calculation of the lattice dynamical properties of superconducting MgCNi3 has been performed using density functional perturbation theory (DFPT). The calculated phonon dispersion curves and phonon density of states have been compared with inelastic x-ray scattering (IXS) and inelastic neutron scattering (INS) measurements. We show for the first time that phonon dispersion curves for MgCNi3 in whole Brillouin zone are positive (stable phonon modes) and in good agreement with the experimental data. The phonon DOS shows absence of phonon density of states at zero energy unlike earlier calculations. There is a good agreement between calculated and experimental electron-phonon parameter and superconducting transition temperature. The Eliasberg function is quantitatively as well as qualitatively different from the phonon density of states. The lattice specific heat and Debye temperature do not show any anomalous behaviour.

Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

High pressure study on the phonon spectra and thermal properties in hafnium nitride and zirconium nitride

We report ab initio calculations of the thermal properties for transition metal nitrides, hafnium and zirconium nitride at ambient and high pressures. The assessment of thermodynamical properties like lattice specific heat, vibrational energy, internal energy and entropy for two nitrides has been carried out. The basic calculations of ingredient phonon density of states for the determination of thermal properties have been done using density functional perturbation theory including external perturbations like strains and electric fields in periodic systems. The ground state properties such as equilibrium lattice constants and bulk modulus obtained for two nitrides are in good agreement with the available experimental value. The calculated pressure variation of the phonon density of states shows trend similar to the experimental pressure dependent Raman spectra. The lattice specific heat, internal energy, entropy and Helmholtz energy increases with pressure.

STRUCTURAL AND ELECTRONIC PROPERTIES AND PHONONS OF PLATINUM NITRIDES BY DENSITY FUNCTIONAL THEORY

Using first principles calculations, we provide here a unified study of structural and electronic properties along with frequency of phonon modes at some high-symmetry points of the Brillouin zone for the noble metal nitride platinum nitride (PtN) by using PWSCF code. Our calculations are performed for two phases viz. zincblende and rocksalt. The present study predicts the zincblende structure as the most probable crystal structure out of two, besides it being metallic. The calculated structural and electronic properties and zone centre phonon modes are in good agreement with the experimental and other calculated data.

An ab initio study of ground state, electronic and thermodynamical properties of GaP and Ga2P

In the present paper, we report an ab initio calculation of the ground state, electronic and thermodynamical properties like constant volume lattice specific heat, vibrational energy, internal energy, and entropy for GaP and Ga2P is presented. These properties are obtained after calculating the phonon spectrum over the entire Brillouin zone. The calculations were performed using the ABINIT program package, which is based on density functional theory (DFT) method and the use of pseudopotentials and plane wave expansion. Difference in the ground state properties such as electronic structure and thermodynamical properties are discussed. The thermodynamical properties follow the expected trend. There is a good agreement between present theoretical and limited available experimental data in the case of ground state such as lattice constant and bulk modulus and electronic properties. With the increase of Ga atoms in the unit cell the semiconducting nature of Ga2P turns to metallic. There is a noticeable difference in the thermodynamical properties in the case of both gallium compounds.

Pressure-induced vibrational and electronic properties of palladium per nitride

We predict electronic and structural phase transition at 11GPa for crystalline PdN2 in pyrite structure by employing first principles calculation using density functional theory implemented in Quantum Espresso code. The electronic band structure, equation of states and dynamical properties at zero as well as high pressure are calculated within the frame work of conventional GGA exchange correlation functional. We report the sharp change of the Pd-N and N-N bond length at phase transition pressure in support of isostructural phase transition driven by electronic phase transition for PdN2 in pyrite structure. The calculated Raman frequencies near the phase transition pressure reveals the first order isostructural phase transition by the instability of longitudinal acoustical as well as optical branches, provides the mechanism for experimentally observed decomposition below 13GPa.

Pressure-induced phonon, electronic and thermal properties of antiperovskite AlCNi3

First principle pseudopotential calculations were performed to investigate structural, electronic, vibrational, and electron phonon interaction of antiperovskite AlCNi3. The stability of AlCNi3 in the antipervoskite phase has been analysed on the basis of the results of electronic structure, electronic density of states and phonon calculation at ambient as well as hydrostatic 7.3 GPa high pressure. The dynamical stability, electron phonon interaction and superconductivity have been discussed at ambient as well as hydrostatic high pressure 7.3 GPa.

High Pressure Study on The Phonon Spectra in Hafnium Nitrides

We report ab initio calculations of the phonon spectra for hafnium nitride (HfN) at ambient and high pressures. The calculation of phonon density of states using the density functional perturbation theory including external perturbations like strains and electric fields in periodic systems carried out for full Brillouin zone. The lattice constant obtained for the HfN is in agreement with the experimental value. The calculated pressure variation of the phonon density of states show trend similar to the pressure dependent Raman spectra. The results regarding zone‐center phonon modes for HfN shows generally good agreement with Raman measurements phonon.