arXiv subjects

Prashanth Srinivasan

Publications and source records attributed to Prashanth Srinivasan.

4 recordsLinked to original sources

arXiv2026

Multiscale modelling of diffusion and retention of hydrogen in multi-occupancy traps in irradiated bcc metals

We use molecular dynamics simulations to directly compute the effective diffusivity of hydrogen gas atoms in homogeneous distributions of monovacancies in tungsten and vanadium, and voids in tungsten. Rather than fitting the results to an Arrhenius law, we compare to an analytic approximation for the effective diffusivity recently derived for multi-occupancy traps [Kaur et al (2025), Phys. Rev. Mater. 9:125404]. We find good agreement between full atomistic simulation and our theory, validating the analytic model for diffusivity for materials containing nanoscale defects characteristic of radiation damage. There are no parameters fitted, only physically motivated quantities that can be computed with static density functional or atomistic potential calculations. In this study we prove rapid convergence of hydrogen trap occupation to the steady state using lattice kinetic Monte Carlo, the spontaneous emergence of voids in tungsten using atomistic simulation with empirical potentials, and molecular hydrogen formation in voids using molecular dynamics. We conclude with a prediction for diffusion and retention of hydrogen in voids in tungsten starting from first principles. This work shows that not only is the analytic form for diffusivity and retention in multi-occupancy traps a practical scheme for making predictive simulations of hydrogen isotope diffusion and retention in irradiated microstructures, derived and parameterized from first principles, it is superior to existing single-occupancy trap formalisms.

cond-mat.mtrl-sci↗

arXiv2025

The effect of multi-occupancy traps on the diffusion and retention of multiple hydrogen isotopes in irradiated tungsten and vanadium

We propose a computational scheme for the diffusion and retention of multiple hydrogen isotopes (HI) with multi-occupancy traps parameterized by first principles calculations. We show that it is often acceptable to reduce the complexity of the coupled differential equations for gas evolution by taking the dynamic steady state, a generalisation of the Oriani equilibrium for multiple isotopes and multi-occupancy traps. The effective gas diffusivity varies most with mobile fraction when the total gas concentration approximates the trap density. We show HI binding to a monovacancy in vanadium produces a non-monotonic dependence between diffusivity and gas concentration, unlike the tungsten system. We demonstrate the difference between multiple single occupancy traps and multi-occupancy traps in long-term diffusion dynamics. The applicability of the multi-occupancy, multi-isotope model in steady state is assessed by comparison to an isotope exchange experiment between hydrogen and deuterium in self-ion irradiated tungsten. The vacancy distribution is estimated with molecular dynamics, and the retention across sample depth shows good agreement with experiment using no fitting parameters.

cond-mat.mtrl-sci↗

arXiv2024

Accurate prediction of structural and mechanical properties on amorphous materials enabled through machine-learning potentials: a case study of silicon nitride

Amorphous silicon nitride (a-SiN) is a material which has found wide application due to its excellent mechanical and electrical properties. Despite the significant effort devoted in understanding how the microscopic structure influences the material performance, many aspects still remain elusive. If on the one hand \textit{ab initio} calculations respresent the technique of election to study such a system, they present severe limitations in terms of the size of the system that can be simulated. Such an aspect plays a determinant role, particularly when amorphous structure are to be investigated, as often results depend dramatically on the size of the system. Here, we overcome this limitation by training a machine-learning (ML) interatomic model to \textit{ab initio} data. We show that molecular dynamics simulations using the ML model on much larger systems can reproduce experimental measurements of elastic properties, including elastic isotropy. Our study demonstrates the broader impact of machine-learning potentials for predicting structural and mechanical properties, even for complex amorphous structures.

cond-mat.mtrl-sci↗

arXiv2022

High-accuracy thermodynamic properties to the melting point from ab initio calculations aided by machine-learning potentials

Accurate prediction of thermodynamic properties requires an extremely accurate representation of the free energy surface. Requirements are twofold -- first, the inclusion of the relevant finite-temperature mechanisms, and second, a dense volume-temperature grid on which the calculations are performed. A systematic workflow for such calculations requires computational efficiency and reliability, and has not been available within an ab initio framework so far. Here, we elucidate such a framework involving direct upsampling, thermodynamic integration and machine-learning potentials, allowing us to incorporate, in particular, the full effect of anharmonic vibrations. The improved methodology has a five-times speed-up compared to state-of-the-art methods. We calculate equilibrium thermodynamic properties up to the melting point for bcc Nb, magnetic fcc Ni, fcc Al and hcp Mg, and find remarkable agreement with experimental data. Strong impact of anharmonicity is observed specifically for Nb. The introduced procedure paves the way for the development of ab initio thermodynamic databases.

cond-mat.mtrl-sci↗