arXiv subjects

Balaram Thakur

Publications and source records attributed to Balaram Thakur.

3 recordsLinked to original sources

arXiv2026

Scalar and fully relativistic pressure and temperature-dependent ab-initio thermodynamics study of simple cubic polonium

The ab-initio thermodynamic properties of simple cubic polonium (α-Po) were studied within the quasi-harmonic approximation (QHA), where both lattice vibrations (phonons) and electronic excitations contributions are included in the Helmholtz free energy. We investigate the influence of spin-orbit coupling (SOC) by comparing the scalar relativistic (SR) and fully relativistic (FR) pseudopotentials on the thermodynamic properties of polonium and evaluate the performance of three popular exchange-correlation functionals, GGA (PBE and PBEsol), and LDA (PZ). Temperature and pressure-dependent thermodynamic properties were compared with the available experimental and theoretical studies. We found that the effect of electronic excitations is negligible for all the thermodynamic properties. LDA+SOC provides a better agreement with the experimental volume, while the thermal expansion coefficients from LDA+SOC and PBEsol + SOC closely match experimental values. SOC effects appear insignificant for the isobaric heat capacity but substantially contribute to the adiabatic bulk modulus. The phonon dispersions and mode-Grüneisen parameters (γ_qη) were interpolated at the lattice constant corresponding to 301 K. The SR dispersions exhibit several anomalies in all directions, which were suppressed significantly by the inclusion of SOC. The role of SOC on the elastic constant-coefficient (C_ij) and elastic anisotropy factor at 0 K is also studied. The Pugh ratio confirmed that simple cubic polonium is ductile, and we observed that the elastic anisotropy factor and Pugh ratio decreased with increasing pressure. The effect of SOC on the Cauchy pressure is also determined.

cond-mat.mtrl-sci↗

arXiv2025

Thermodynamic properties of fcc lead: A scalar and fully relativistic first principle study

This study investigates the thermodynamic properties of face-centered cubic lead (fcc-Pb) using ab-initio methods within the quasi-harmonic approximation (QHA), examining the influence of spin-orbit coupling (SOC) and the exchange-correlation functionals. Two types of ultrasoft pseudopotential (US-PP) are considered: one that excludes (scalar relativistic PP) and one that includes the SOC effects (fully relativistic PP). Further, for each PP, we test the performance of three popular exchange-correlation functionals: Perdew-Burke-Ernzerhof generalized gradient approximation (PBE) (Perdew et al. Phys. Rev. Lett. 77, 3865 (1996)), PBE modified for dense solids (PBEsol) (Perdew et al. Phys. Rev. Lett. 100, 136406 (2008)), and local density approximation (LDA) (Perdew et al. Phys. Rev. B 23, 5048 (1981)). We calculate the Helmholtz free energy, incorporating lattice vibrations (phonons) and electronic excitation contributions. The estimated equation of state (at 4 K and 301 K), phonon dispersions (at 100 K and 300 K), mode-Grüneisen parameters (γqη) (at 100 K), volume thermal expansion coefficient (\b{eta}), isobaric heat capacity (CP), bulk modulus (BS), and thermodynamic average Grüneisen parameter (γ) are compared with the available experimental and theoretical studies. Moreover, the 0 K pressure-dependent elastic constant-coefficient (Cij) of fcc lead and Pugh ratio, Debye temperature, and longitudinal and transverse sound velocities for polycrystalline lead are presented. The contributions of electronic excitations in all the thermodynamic properties are found to be negligible. With increasing pressure, the role of spin-orbit effects decreases but does not vanish. Our findings demonstrate that SOC leads to results distinct from the SR approach, but agreement with the experiment is not consistently improved by including SOC.

cond-mat.mtrl-sci↗

arXiv2024

Ab initio thermodynamic properties of Iridium: A high-pressure and high-temperature study

The high-pressure and high-temperature thermodynamic properties of iridium are studied using density functional theory in combination with the quasi-harmonic approximation, where both the contributions to the free energy of phonons and of electronic excitations are considered. The reliability of different exchange and correlational functionals [Perdew-Burke-Ernzerhof generalized gradient approximation (PBE) (Perdew et al. Phys. Rev. Lett. 77, 3865 (1996)), PBE modified for dense solids (PBEsol) (Perdew et al. Phys. Rev. B 100, 136406 (2008)) and local density approximation (LDA) (Perdew et al. Phys. Rev. B 23, 5048 (1981))], for studying the equation of state (EOS), the phonon dispersions, the mode-Grüneisen parameter, and different thermodynamic properties like thermal pressure, volume thermal expansivity, isobaric heat capacity, bulk modulus, and the average Grüneisen parameter are tested. Elastic constants are studied at T=0 K as a function of pressure. The predicted results are compared with the available experiments and previous theoretical data. We find generally a good agreement with experiments with at least one functional, but none of the three outperforms the others in all the investigated thermodynamic properties. The electronic excitations contribution is minimal in bulk modulus, but it is significant for other thermodynamic properties.

cond-mat.mtrl-sci↗