Syed Shovon Mahbub Mahin

arXiv2026

First-principles investigation of structural, mechanical, vibrational, thermal, electronic and optical properties of Na3Bi: a topological Dirac semimetal

Exploring the properties of topological materials has remained an active area of research in condensed matter physics for the past few decades. Here, we present a first-principles investigation of the structural, elasto-mechanical, thermal, electronic, and optical properties of Na3Bi, one of the earliest discovered topological Dirac semimetals, using density functional theory. The hexagonal phase of Na3Bi is found to be both mechanically and dynamically stable, exhibiting moderate elastic anisotropy with a universal anisotropy index of 0.832. The compound displays a moderate machinability index of 2.386 alongside a low hardness value of 2.005, consistent with its predominantly brittle, covalently bonded character accompanied by a slight metallic contribution. Its comparatively low Debye temperature of 181.39K points to a mechanically soft lattice with loosely bound atoms. Electronic structure calculations confirm semimetallic behavior, with well-defined Dirac points pinned at the Fermi level and a Fermi surface composed of point-like pockets. Optical analysis across a wide spectral range reveals non-selective, moderate reflectivity of 40 to 45% and, in the visible region, an unusually high refractive index reaching between 2 and 4.5. Na3Bi is additionally found to be an efficient absorber of ultraviolet radiation. Together, these findings establish a comprehensive baseline for the mechanical, thermal, and optical behavior of hexagonal Na3Bi and point to its potential relevance for acoustic damping, UV-sensing, and optoelectronic applications

cond-mat.mtrl-sci↗

arXiv2025

DFT based insights into elastic, thermophysical, electronic and optical properties of topological insulators XTe5 (X = Zr, Hf)

Transition metal penta-tellurides, ZrTe5 and HfTe5 have been recently drawn a lot of attention due to their fascinating physical properties and for being prominent materials showing topological phase transitions. In this study, we investigated mechanical, thermophysical and optoelectronic properties of these materials which remained almost unexplored till now. We also studied electronic properties and compared those with previous studies. We used Density Functional Theory (DFT) based calculations to study all of these properties. This study suggests that the materials are mechanically stable, possess high mechanical and bonding anisotropy and are brittle in nature. Our study also suggests that the compounds are soft in nature and they contain a mixture of covalent and metallic bonding. Investigation of thermophysical properties, namely, Grüneisen parameter and Debye temperature indicates weak bonding strength in these compounds. Analysis of melting temperature, thermal expansion coefficient, heat capacity, radiation factor, acoustic impedance, and minimum thermal conductivity suggests their possible application in acoustic and thermoelectric devices. Examination of their optical characteristics reveals that they have a considerable reflectivity from the infrared to the ultraviolet region. The refractive indices of these materials are high at low energy so they are potential candidates for reflective coating of solar radiation. There have been debates over exact topological natures of these compounds, whether they are semi-metals or insulators. Our study of electronic band structure and density of states reveal that spin-orbit interaction is responsible for enhancing energy gaps and promoting insulating characteristics in these compounds.

cond-mat.mtrl-sci↗