arXiv subjects

M. Warrier

Publications and source records attributed to M. Warrier.

5 recordsLinked to original sources

arXiv2025

Molecular Dynamics Simulations of Collision Cascades in Niobium: Comparing Interatomic Potentials

Radiation damage in structural materials is a major challenge for advanced nuclear energy systems, and niobium is of particular interest due to its high melting point, mechanical strength, and corrosion resistance. To better understand its radiation response, we carried out large-scale molecular dynamics simulations of collision cascades in pure niobium at 300 K over a primary knock-on atom (PKA) energy range of 1-75 keV, employing four interatomic potentials: an embedded atom method (EAM), two Finnis-Sinclair models (FS-1 and FS-2), and a machine learning-based spectral neighbor analysis potential (SNAP) we developed. All reproduce the general features of cascade formation but differ significantly in defect production, clustering, and morphology. At low energies, defect generation follows trends governed by threshold displacement energy (TDE) and the stiffness-to-range ratio (|S/R|). At higher energies, subcascade formation makes defect evolution dependent on the combined effects of |S/R|, average TDE, and other material-specific factors. Vacancy clustering dominates over interstitial clustering across all cases: EAM produces the largest vacancy clusters and the highest clustering fraction, while SNAP shows the strongest interstitial clustering. Morphological analysis indicates that EAM forms a balanced mix of 1/2<111>, 1/2<110> loops, C15 rings, and hybrid structures; FS-2 favors extended 1/2<111> dumbbells, crowdions, and dislocation loops; whereas FS-1 and SNAP generate more compact or disordered clusters, with SNAP produces a high fraction of C15-like rings (maximum size up to nine atoms) that may evolve into dislocation loops of 1/2<111> and <100>. These findings give clear insights into how niobium reacts when exposed to irradiation, especially at high energies.

cond-mat.mtrl-sci↗

arXiv2024

Statistical Study of the Defect Cluster Morphology in the Primary Damage of Tungsten from Collision Cascades from Five Inter-atomic potentials

The size and morphology of defect clusters formed during primary damage play a crucial role in the subsequent microstructural evolution of irradiated materials. Molecular dynamics (MD) simulations of collision cascades in tungsten (W) were performed using five interatomic potentials (IAPs): the quantum-accurate machine-learned Spectral Neighbor Analysis Potential (W-SNAP), the machine learning-based tabGAP potential, and three embedded-atom method (EAM) potentials. A total of 3,500 MD simulations were conducted with primary knock-on atoms (PKAs) at energies of 5, 10, 20, 50, 75, 100, and 150 keV. PKAs were launched in 100 random directions at each energy to ensure statistical validity. Analysis was performed using CSaransh , a web-based tool for large-scale collision cascade databases, to quantify: (i) the number of defects (isolated and clustered), (ii) defect cluster morphologies, (iii) defect cluster size distributions and (iv) the number of sub-cascades formed. We show that the difference in the formation energy of self interstitial atom dumbells along the <1 1 0> and <1 1 1> directions critically influence defect cluster morphology. Our results indicate that IAP stiffness and interaction range independently do not affect defect count. However, these parameters combined with defect formation energies, threshold displacement energies, and other factors significantly influence defect production.

cond-mat.mtrl-sci↗

arXiv2022

Multi-scale modelling to estimate spall parameters in metallic single crystals

Modeling dynamics fracture in materials involves usage of hydrodynamic codes which solve basic conservation laws of mass, energy and momentum in space and time. This requires appropriate models to handle elastic-plastic deformation, equation of state, material strength, and fracture. Nucleation and Growth (NAG) damage model is a micro-physical model which computes amount of damage in the material by accounting for phenomena like nucleation, growth and coalescence of voids or cracks. The NAG model involves several material model parameters, such as nucleation threshold, growth threshold, etc. Traditionally these parameters are fitted to experimental void volume distributions. In the present paper we fit these parameters to molecular dynamics (MD) simulations of void nucleation and growth and use the fitted parameters in hydrodynamic simulations in a multi-scale computational approach. Cubic metallic single crystals are subjected to isotropic deformation and the nucleation of voids and their growth were post-processed from the simulations. These results are used in an in-house Particle Swarm Optimization (PSO) code to obtain NAG parameters for materials of our interest. Using these parameters in a 1D hydrodynamic code developed in-house, fracture parameters such as spall strength and thickness are obtained. The results are validated with published experimental data for Mo, Nb and Cu which have been simulated using the multi-scale model. This paper describes the application of the multi-scale model to obtain the NAG fracture model parameters of Al and its spall data. The results are compared with published experimental results in single crystal Al.

cond-mat.mtrl-sci↗

arXiv2021

Simulation of 2D ballistic deposition of porous nanostructured thin-films

A "two-dimensional ballistic deposition" (2D-BD) code has been developed to study the geometric effects in ballistic deposition of thin-film growth. Circular discs are used as depositing specie to understand the shadowing effects during the evolution of a thin-film. We carried out the 2D-BD simulations for the angles of deposition $20^0$-$80^0$ in steps of $10^0$. Standard deviations $1^0$, $2^0$, $4^0$, $6^0$ and $10^0$ are used for each angle of deposition with disc size of $1.5 \overset{\circ}{A}$ to understand its effect on the microstructure of the thin-films. Angle of growth, porosity and surface roughness properties have been studied for the afore-mentioned angles of deposition and their standard deviations. Ballistic deposition simulations with the discs of different sizes have been carried out to understand the effect of size in ballistic deposition. The results from this code are compared with the available theoretical and experimental results. The code is used to simulate a collimated glancing angle deposition (C-GLAD) experiment. We obtain a good qualitative match for various features of the deposits.

physics.comp-ph↗

arXiv2020

Inclusion and validation of electronic stopping in the open source LAMMPS code

Electronic stopping (ES) of energetic atoms is not taken care of by the interatomic potentials used in molecular dynamics (MD) simulations when simulating collision cascades. The Lindhard-Scharff (LS) formula for electronic stopping is therefore included as a drag term for energetic atoms in the open source large scale atomic molecular massively parallel simulator (LAMMPS) code. In order to validate the ES implementation, MD simulations of collision cascades at primary knock-on atom (PKA) energies of 5, 10 and 20 keV are carried out in W and Fe in 100 random directions. The total ES losses from the MD simulations show energy straggling due to the stochastic nature of the phenomena. Thelosses due to ES are compared with that predicted by theNorgett-Robinson-Torrens (NRT) model to validate our implementation. It is seenthat the root mean square deviation of ES losses from the MD implementation is around 10 \% for both W and Fe compared to the NRT model. The velocity threshold above which electronic stopping is important is explored. The effect of ES on the number of defects in collision cascades is presented for Fe and W.

physics.comp-ph↗