MEAMfit: A reference-free modified embedded atom method (RF-MEAM) energy and force-fitting code

Abstract

Ab initio modeling of materials has become routine in recent years, largely due to the success of density functional theory (DFT). However, for many processes in materials, realism is achieved only when millions of atoms are considered. Currently, such large scale simulations are beyond ab initio capabilities so that one has to resort to effective interatomic potentials that well represent ab initio data on smaller scales. Two of the more widely used types of interatomic potentials are embedded atom method (EAM) and modified embedded atom method (MEAM) potentials. Here we present a code that can use ab initio generated energies and forces to obtain representative EAM and reference-free MEAM type effective interatomic potentials. We illustrate the use of this code with ab initio computed thermal excitations in ZrC

Fast anharmonic free energy method with an application to vacancies in ZrC

“…The interatomic potentials are generated using a genetic-algorithm conjugate-gradient fitting procedure implemented and publicly available in the MEAMFIT2 code. [24][25][26] The code fits an RF-MEAM potential that permits locally positive and negative density terms in order to increase variational freedom, subject to a net positive background. The fitted potential has 3 embedding and 3 pairwise terms, within a radial cutoff of 4.8 Å, which includes interactions up to third nearest-neighbor.…”

Ab initio vibrational free energies including anharmonicity for multicomponent alloys

“…We thus investigate whether an EAM fit for the complex disordered VNbMoTaW HEA is possible and, if it is, how it performs for thermodynamic integration. We employ the meamfit v2 package [50,51]. Our tests show that the number of expansion parameters has only a small influence [26].…”

Improved method of calculatingab initiohigh-temperature thermodynamic properties with application to ZrC

“…The gain in efficiency, although not the value of the final free energy, should depend to some extent on the potential used for the intermediate reference state, for which we adopted a MEAM potential, fitted to the energies of molecular dynamics configurations close to the melting point. The MEAMfit code [22] is freely available for this purpose. Our procedure will be generally applicable to other ultrahightemperature ceramics, and indeed to a wide range of materials.…”

“…The MEAM potentials were optimized using the MEAMfit fitting code [22], with the variance in the error of the fitted energies taken as the objective function to be minimized:…”