arXiv subjects

Sabyasachi Tiwari

Publications and source records attributed to Sabyasachi Tiwari.

12 recordsLinked to original sources

arXiv2026

First-principles predictions of carrier mobility with record accuracy using GW perturbation theory

Accurate prediction of carrier mobility is critical for the discovery and design of next-generation electronic materials. Despite sustained progress, state-of-the-art ab initio methods remain limited by the approximate treatment of electron-phonon interactions at the density functional theory level. Here, we demonstrate that incorporating many-body GW corrections to both the electronic band structure and electron--phonon couplings when solving the ab initio Boltzmann transport equation yields a mean absolute relative error of just 11% for electron mobilities across benchmark semiconductors, including Si, GaAs, GaP, diamond, and SiC. The common practice of neglecting GW corrections to the electron--phonon interaction can lead to mobility errors exceeding 50%. The present findings highlight the importance of many-body GW self-energy effects in carrier transport simulations, and provides fundamental insights into how many-body electron--phonon interactions govern charge transport in crystalline solids.

cond-mat.mtrl-sci↗

arXiv2026

First-principles carrier mobility and optical absorption of strained ZnO with self-consistent Hubbard interactions

Carrier mobility and optical absorption are key performance parameters of oxide semiconductors in transparent and flexible displays. We use a newly developed density-functional perturbation theory with a self-consistent Hubbard correction (DFPT+U) to study phonon-limited electron transport and phonon-assisted optical absorption in strained zinc oxide (ZnO). This parameter-free approach accounts for electron-phonon interactions and on-site correlation effects simultaneously. Electronic structures and phonon dispersions are computed under three distinct uniaxial strain directions. Uniaxial tensile strain up to 4.8% along [\bar110] is found to increase the room-temperature electron mobility by 19% while leaving visible-range optical absorption essentially unchanged. These results demonstrate that moderate strain can selectively enhance carrier transport without degrading optical transparency, and establish DFPT+U as an effective framework for predicting strain-dependent transport and optical properties in wide-band-gap oxides with implications for strain-engineered display and optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Meta-optimization of maximally-localized Wannier functions

Maximally-localized Wannier functions are quantum wavefunctions resembling atomic orbitals that are used to describe electrons in condensed matter. Since their introduction in 1997, these functions have become ubiquitous in ab initio materials simulations, including applications in linear-scaling methods, strongly-correlated electron systems, quantum transport, electron-phonon interactions, and topological materials. Despite their widespread adoption in a vast software ecosystem, Wannier functions have not yet attained their fullest potential in the presence of entangled bands, as their optimization remains challenging and labor-intensive. Here, we introduce a universal meta-optimization method that leverages workflow abstraction and machine learning techniques like differential evolution and Bayesian optimization to generate globally optimized Wannier functions without human intervention. We demonstrate this approach through three applications: (i) autonomous interpolation of entangled band structures with millielectronvolt accuracy starting from coarse Brillouin zone grids, (ii) thousand-fold acceleration of fully ab initio Boltzmann transport calculations via the use of minimal coarse Brillouin zone grids, and (iii) ultra-fast high-throughput calculations of high-precision Wannier functions for large materials libraries. This work brings calculations that previously required supercomputers within the reach of personal computers.

physics.comp-ph↗

arXiv2026

Electron-phonon physics at the exascale: A hybrid MPI-GPU-OpenMP framework for scalable Wannier interpolation

We demonstrate a highly efficient GPU implementation of the Wannier interpolation of electron-phonon matrix elements in the EPW code. Building on a systematic analysis of the computational complexity of the algorithm for electron-phonon interpolation, we designed a GPU porting strategy that integrates naturally into the current EPW implementation, and is seamlessly portable to NVIDIA, AMD, and Intel GPUs. We demonstrate this development via extensive benchmarks on conventional semiconductors such as silicon and monolayer MoS$_2$, as well as a large-scale application to topological stanene nanoribbons of width as large as 20nm, which was intractable with previous implementations. Compared to the single MPI parallelization scheme of EPW v5.9, the resulting hybrid MPI-GPU-OpenMP scheme achieves up to 29-fold speedup on leadership-class supercomputers equipped with NVIDIA and Intel accelerators, namely Vista at the Texas Advanced Computing Center, Perlmutter at the National Energy Research Scientific Computing Center, and Aurora at the Argonne Leadership Computing Facility. This framework also achieves nearly ideal scalability up to thousands of GPU nodes on the Aurora supercomputer. With this development, EPW is ready to support electron-phonon physics calculations on exascale platforms.

cond-mat.mtrl-sci↗

arXiv2025

EPW-VASP interface for first-principles calculations of electron-phonon interactions

We present an interface between the Vienna \textit{Ab initio} Simulation Package (VASP) and the EPW software for calculating materials properties governed by electron-phonon (e-ph) interactions. Computation of the e-ph matrix elements with the finite-difference supercell approach in VASP and their fine-grid interpolation in EPW enable accurate modeling of temperature-dependent materials properties and phonon-assisted quantum processes with VASP's extensive library of exchange-correlation functionals and pseudopotentials. We demonstrate the functionality of the EPW-VASP interface by examining the superconducting gap and critical temperature in MgB$_2$ using the anisotropic Migdal-Eliashberg equations, and the carrier mobility in cubic BN using the \textit{ab initio} Boltzmann transport equation.

cond-mat.mtrl-sci↗

arXiv2025

Comparative study of phonon-limited carrier transport in the Weyl semimetal TaAs family

We present a systematic first-principles study of phonon-limited transport in the TaAs family of Weyl semimetals using the ab initio Boltzmann transport equation. The calculated electrical conductivities show excellent agreement with experimental data for high-quality samples, confirming that transport in these systems is predominantly limited by phonon scattering. Among the four compounds, NbP achieves the highest conductivity, governed primarily by its large Fermi velocities that offset its stronger scattering rates. In contrast, TaAs displays the lowest conductivity, linked to reduced carrier pockets and limited carrier velocities. Additionally, NbP conductivity remains largely unaffected by small hole or electron doping, whereas TaAs exhibits pronounced electron-hole asymmetry. NbAs and TaP show intermediate behavior, reflecting their Fermi surface topologies and scattering phase space. These findings provide microscopic insight into the transport mechanisms of the TaAs family and emphasize the critical role of phonons, doping, and carrier dynamics in shaping their electronic response.

cond-mat.mes-hall↗

arXiv2025

First-principles electron-phonon interactions with self-consistent Hubbard interaction: an application to transparent conductive oxides

The ab initio computational method known as Hubbard-corrected density functional theory (DFT+$U$) captures well ground electronic structures of a set of solids that are poorly described by standard DFT alone. Since lattice dynamical properties are closely linked to electronic structures, the Hubbard-corrected density functional perturbation theory (DFPT+$U$) can calculate them at the same level of accuracy. To investigate the effects of $U$ on electron-phonon (el-ph) interactions, we implemented DFPT+$U$ with a Hartree-Fock-based pseudohybrid functional formalism to determine $U$ self-consistently and applied our method to compute optical and transport properties of transparent conductive oxides of CdO and ZnO. For CdO, we find that opening a band gap due to $U$ restores the long-range Fröhlich interaction and that its calculated mobility and absorption spectrum are in excellent agreement with experiments. For ZnO where a band gap already appears at the DFT level, DFPT+$U$ brings the results into much closer alignment with experiment, thus demonstrating improved accuracy of our method in dealing with el-ph interactions in these technologically important materials.

cond-mat.mtrl-sci↗

arXiv2023

Reduction of Magnetic Interaction Due to Clustering in Doped Transition-Metal Dichalcogenides: A Case Study of Mn, V, Fe-Doped $\rm WSe_2$

Using Hubbard U corrected density functional theory calculations, lattice Monte-Carlo, and spin-Monte-Carlo simulations, we investigate the impact of dopant clustering on the magnetic properties of WSe2~doped with period four transition metals. We use manganese (Mn) and iron (Fe) as candidate n-type dopants and vanadium (V) as the candidate p-type dopants, substituting the tungsten (W) atom in WSe2. Specifically, we determine the strength of the exchange interaction in the Fe-, Mn-, and V-doped WSe2~ in the presence of clustering. We show that the clusters of dopants are energetically more stable than discretely doped systems. Further, we show that in the presence of dopant clustering, the magnetic exchange interaction significantly reduces because the magnetic order in clustered WSe2~becomes more itinerant. Finally, we show that the clustering of the dopant atoms has a detrimental effect on the magnetic interaction, and to obtain an optimal Curie temperature, it is important to control the distribution of the dopant atoms.

cond-mat.mtrl-sci↗

arXiv2022

Atomistic modeling of spin and electron dynamics in two-dimensional magnets switched by two-dimensional topological insulators

To design fast memory devices, we need material combinations which can facilitate fast read and write operation. We present a heterostructure comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as a viable option for designing fast memory devices. We theoretically model spin-charge dynamics between the 2D magnets and 2D TIs. Using the adiabatic approximation, we combine the non-equilibrium Green's function method for spin-dependent electron transport, and time-quantified Monte-Carlo for simulating magnetization dynamics. We show that it is possible to switch the magnetic domain of a ferromagnet using spin-torque from spin-polarized edge states of 2D TI. We further show that the switching between TIs and 2D magnets is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an optimal interface exchange depending on the exchange interaction within the magnet is required for efficient switching. Finally, we compare the experimentally grown Cr-compounds and show that Cr-compounds with higher anisotropy (such as $\rm CrI_3$) results in lower switching speed but more stable magnetic order.

cond-mat.mes-hall↗

arXiv2021

Computing Curie temperature of two-dimensional ferromagnets in the presence of exchange anisotropy

We compare three first-principles methods of calculating the Curie temperature in two-dimensional (2D) ferromagnetic materials (FM), modeled using the Heisenberg model, and propose a simple formula for estimating the Curie temperature with high accuracy that works for all common 2D lattice types. First, we study the effect of exchange anisotropy on the Curie temperature calculated using the Monte-Carlo (MC), the Green's function method, and the renormalized spin-wave (RNSW). We find that the Green's function overestimates the Curie temperature in high-anisotropy regimes compared to MC, whereas RNSW underestimates the Curie temperature compared to the MC and the Green's function. Next, we propose a closed-form formula for calculating the Curie temperature of 2D FMs, which provides an estimate of the Curie temperature greatly improving over the mean-field expression for magnetic material screening. We apply the closed-form formula to predict the Curie temperature 2D magnets screened from the C2DB database and discover several high Curie temperature FMs with Fe2F2 and MoI2 emerging as the most promising 2D ferromagnets. Finally, comparing to experimental results for CrI3, CrCl3, and CrBr3, we conclude that for small effective anisotropies, the Green's function-based equations are preferable, while, for larger anisotropies MC-based results are more predictive.

cond-mat.mtrl-sci↗

arXiv2021

Critical behavior of ferromagnets CrI3, CrBr3, CrGeTe3, and anti-ferromagnet FeCl2: a detailed first-principles study

We calculate the Curie temperature of layered ferromagnets, chromium tri-iodide (CrI3), chromium tri-bromide (CrBr3), chromium germanium tri-telluride (CrGeTe3), and the Neel temperature of a layered anti-ferromagnet iron di-chloride (FeCl2), using first-principles density functional theory calculations and Monte-Carlo simulations. We develop a computational method to model the magnetic interactions in layered magnetic materials and calculate their critical temperature. We provide a unified method to obtain the magnetic exchange parameters (J) for an effective Heisenberg Hamiltonian from first-principles, taking into account both the magnetic ansiotropy as well as the out-of-plane interactions. We obtain the magnetic phase change behavior, in particular the critical temperature, from the susceptibility and the specific-heat, calculated using the three-dimensional Monte-Carlo (Metropolis) algorithm. The calculated Curie temperatures for ferromagnetic materials (CrI3, CrBr3 and CrGeTe3), match very well with experimental values. We show that the interlayer interaction in bulk CrI3 with R3 stacking is significantly stronger than the C2/m stacking, in line with experimental observations. We show that the strong interlayer interaction in R3 CrI results in a competition between the in-plane and the out-of-plane magnetic easy axis. Finally, we calculate the Neel temperature of FeCl2 to be 47 +- 8 K, and show that the magnetic phase transition in FeCl2 occurs in two steps with a high-temperature intralayer ferromagnetic phase transition, and a low-temperature interlayer anti-ferromagnetic phase transition.

cond-mat.mes-hall↗

arXiv2018

Theoretical studies of electronic transport in mono- and bi-layer phosphorene: A critical overview

Recent $\textit{ab initio}$ theoretical calculations of the electrical performance of several two-dimensional materials predict a low-field carrier mobility that spans several orders of magnitude (from 26,000 to 35 cm$^{2}$ V$^{-1}$ s$^{-1}$, for example, for the hole mobility in monolayer phosphorene) depending on the physical approximations used. Given this state of uncertainty, we review critically the physical models employed, considering phosphorene, a group V material, as a specific example. We argue that the use of the most accurate models results in a calculated performance that is at the disappointing lower-end of the predicted range. We also employ first-principles methods to study high-field transport characteristics in mono- and bi-layer phosphorene. For thin multi-layer phosphorene we confirm the most disappointing results, with a strongly anisotropic carrier mobility that does not exceed $\sim$ 30 cm$^{2}$ V$^{-1}$ s$^{-1}$ at 300 K for electrons along the armchair direction.

cond-mat.mes-hall↗