arXiv subjects

Abhiyan Pandit

Publications and source records attributed to Abhiyan Pandit.

8 recordsLinked to original sources

arXiv2026

Metal hydrides achieve high-Tc superconductivity at low pressure by mimicking high-pressure H3S chemical bonding

Compressed hydrides are promising candidates for high-temperature superconductivity, yet achieving simultaneous structural stability and high-Tc at low pressures remains challenging. Here, we introduce a new mechanism for accomplishing this goal by mimicking the bonding characteristics of high-pressure H3S within metal hydrides. Using Li3CuH4 as an example, its Cu-H covalent interaction effectively mimics the core function of the S-H bonding in H3S. This interaction not only induces a high hydrogen-derived electronic density of states at the Fermi level, but also softens the hydrogen phonon modes, thereby significantly enhancing the electron-phonon coupling. Furthermore, embedding the strongly ionic Li3H lattice into the covalent Cu-H framework stabilizes the structure at significantly low pressures via a chemical-template effect, while maintaining high-Tc. Li3CuH4 exhibits excellent thermodynamic stability at 20 GPa, with a Tc of 39.25 K at 12 GPa. Further comprehensive high-throughput studies on Li3MH4 (M = transition metal) compounds uncover general principles applicable to a broader range of compounds. This work establishes a new paradigm for the simultaneous optimization of the stability and high-temperature superconductivity of metal hydrides through complementary sublattice interactions, thus advancing the search for practical and viable superconducting materials.

cond-mat.supr-con↗

arXiv2025

Non-local Chemistry Driven by Cation-Anion Size Disparity in Helium Inserted Compounds under High Pressure

Opposing the theory that Helium (He) cannot be inserted into AB-type ionic compounds due to the Madelung energy increase, our crystal structure search and first-principles calculations found that He can form stable compounds with sodium halides (NaX, X=Cl, Br, I) under high-pressure. These reactions are driven by the non-local chemistry arising from the cation-anion size disparity, distinctly different from the He insertion reaction with A2B-type compounds. The large size differences between Na+ and X- enable structures that can effectively host He insertions through volume and inter-atomic distance disproportionation. Furthermore, the insertion of He atoms can significantly relieve the elevated Madelung energy that builds up in NaX under high pressure. This energy increase arises from structural transitions driven by cation-anion size disparity, which are necessary for reducing volume under pressure. The insertion of He allows the reduction of the total volume under high pressure without increasing the Madelung energy. Our predicted compounds and stability analysis reveal a new example of He reactivity governed not by local chemical bond formation, but by long-range electrostatic interactions.

cond-mat.mtrl-sci↗

arXiv2025

First-principles calculation of higher-order elastic constants from divided differences

A method is presented to calculate from first principles the higher-order elastic constants of a solid material. The method relies on finite strain deformations, a density functional theory approach to calculate the Cauchy stress tensor, and a recursive numerical differentiation technique homologous to the divided differences polynomial interpolation algorithm. The method is applicable as is to any material, regardless its symmetry, to calculate elastic constants of, in principle, any order. Here, we introduce conceptual framework and technical details of our method, we discuss sources of errors, we assess convergence trends, and we present selected applications. In particular, our method is used to calculate elastic constants up to the 6$^{th}$ order of two crystalline materials with the cubic symmetry, silicon and gold. To demonstrate general applicability, our method is also used to calculate the elastic constants up to the 5$^{th}$ order of $α$-quartz, a crystalline material belonging to the trigonal crystal system, and the second- and third-order elastic constants of kevlar, a material with an anisotropic bonding network. Higher order elastic constants computed with our method are validated against density functional theory calculations by comparing stress responses to large deformations derived within the continuum approximation.

cond-mat.mtrl-sci↗

arXiv2023

A first-principles method to calculate fourth-order elastic constants of solid materials

A first-principles method is presented to calculate elastic constants up to the fourth order of crystals with the cubic and hexagonal symmetries. The method relies on the numerical differentiation of the second Piola-Kirchhoff stress tensor and a density functional theory approach to compute the Cauchy stress tensors for a minimal list of strained configurations of a reference state. The number of strained configurations required to calculate the independent elastic constants of the second, third, and fourth order is 24 and 37 for crystals with the cubic and hexagonal symmetries, respectively. Here, this method is applied to five crystalline materials with the cubic symmetry (diamond, silicon, aluminum, silver, and gold) and two metals with the hexagonal close packing structure (beryllium and magnesium). Our results are compared to available experimental data and previous computational studies. Calculated linear and nonlinear elastic constants are also used, within a nonlinear elasticity treatment of a material, to predict values of volume and bulk modulus at zero temperature over an interval of pressures. To further validate our method, these predictions are compared to results obtained from explicit density functional theory calculations.

cond-mat.mtrl-sci↗

arXiv2022

Anharmonic effects on lattice dynamics and thermal transport of two-dimensional InTe Monolayer

The lattice thermal conductivity plays a key role in the performance of thermoelectric materials, where the lower values lead to a higher figure of merit values. Two-dimensional group III-VI monolayers such as InTe are promising materials for TE energy generation owing to their low that leads to high TE figure of merit values. In this work, we investigate the influence of the lattice anharmonicity on the lattice thermal conductivity of the InTe monolayer. The thermodynamic parameters are calculated by using the self-consistent phonon theory. The lattice thermal conductivity value of the InTe monolayer is obtained to be 0.30 by using the standard Boltzmann transport equation (BTE) approach, while it is 3.58 by using SCP + BTE approach. These results confirm the importance of the anharmonic effects on the lattice thermal conductivity value, where it was found to be significantly higher (91%) using the SCP + BTE approach than that obtained using the standard BTE approach.

physics.comp-ph↗

arXiv2021

The effect of finite-temperature and anharmonic lattice dynamics on the thermal conductivity of ZrS2 monolayer: self-consistent phonon calculations

Two-dimensional (2D) ZrS2 monolayer (ML) has emerged as a promising candidate for thermoelectric (TE) device applications due to its high TE figure of merit, which is mainly contributed by its inherently low lattice thermal conductivity. This work investigates the effect of the lattice anharmonicity driven by temperature-dependent phonon dispersions on thermal transport of ZrS2 ML. The calculations are based on the self-consistent phonon (SCP) theory to calculate the thermodynamic parameters along with the lattice thermal conductivity. The higher- order (quartic) force constants were extracted by using an efficient compressive sensing lattice dynamics technique, which estimates the necessary data based on the emerging machine learning program as an alternative of computationally expensive density functional theory calculations. Resolve of the degeneracy and hardening of the vibrational frequencies of low-energy optical modes were predicted upon including the quartic anharmonicity. As compared to the conventional Boltzmann transport equation (BTE) approach, the lattice thermal conductivity of the optimized ZrS2 ML unit cell within SCP + BTE approach is found to be significantly enhanced (e.g., by 21% at 300 K). This enhancement is due to the relatively lower value of phonon linewidth contributed by the anharmonic frequency renormalization included in the SCP theory. Mainly, the conventional BTE approach neglects the temperature dependence of the phonon frequencies due to the consideration of harmonic lattice dynamics and treats the normal process of three-phonon scattering incorrectly due to the use of quasi-particle lifetimes. These limitations are addressed in this work within the SCP + BTE approach, which signifies the validity and accuracy of this approach.

cond-mat.mtrl-sci↗

arXiv2020

Thermal conductivity and enhanced thermoelectric performance of SnTe bilayer

Tin chalcogenides (SnS, SnSe, and SnTe) are found to have improved thermoelectric properties upon the reduction of their dimensionality. Here we found the tilted AA + s stacked two-dimensional (2D) SnTe bilayer as the most stable phase among several stackings as predicted by the structural optimization and phonon transport properties. The carrier mobility and relaxation time are evaluated using the deformation potential theory, which is found to be relatively high due to the high 2D elastic modulus, low deformation potential constant, and moderate effective masses. The SnTe bilayer shows a high Seebeck coefficient, high electrical conductivity, and ultralow lattice thermal conductivity. High TE figure of merit (ZT) values, as high as 4.61 along the zigzag direction, are predicted for the SnTe bilayer. These ZT values are much enhanced as compared to the bulk as well as monolayer SnTe and other 2D compounds.

cond-mat.mtrl-sci↗

arXiv2020

Thermoelectric and lattice dynamics properties of layered MX (M = Sn, Pb; X = S, Te) compounds

Lead and tin chalcogenides have been studied widely due to their promising thermoelectric (TE) properties. Further enhancement in their TE efficiency has been reported upon the reduction of the dimension, which is an important feature in modern device fabrications. Using density functional theory combined with the Semi-classical Boltzmann transport theory, we studied the structural, electronic and TE properties of two-dimensional (2D) MX (M = Sn, Pb; X = S, Te) monolayers. Spin-orbit coupling was found to have significant effects on their electronic structure, particularly for the heavy compounds. Structural optimization followed by phonon transport studies prevailed that the rectangular (γ-) phase is energetically the most favorable for SnS and SnTe monolayers, whereas the square structure is found the most stable for PbS and PbTe monolayers. Our results are in good agreement with previous studies. These 2D materials exhibit high Seebeck coefficients and power factors along with low lattice thermal conductivities, which are essential features of good TE materials. The maximum figure of merits (ZT) of 1.04, 1.46, 1.51 and 1.94 are predicted for n-type SnS, SnTe, PBS and p-type PbTe monolayers respectively at 700 K, which are higher than their bulk ZT values. Hence, these monolayers are promising candidates for TE applications.

cond-mat.mtrl-sci↗