The selection of interatomic potentials for simulation of extreme actions within the tungsten lattice

Simulation of crystal lattices under conditions far from equilibrium is an increasingly important subject of research and requires confidence in the validity of the applied interatomic potentials in a wide range of atom deviations from the balanced condition. To make such an assessment for modeling tungsten as an advanced material for various nuclear applications, the authors analyzed the nonlinear behavior of the lattice using several interatomic potentials. In a bcc tungsten crystal, oscillations were simulated according to the laws of several delocalized nonlinear vibrational modes – exact solutions to the equations of motion of atoms, the geometry of which is determined by the lattice symmetry at any amplitudes and does not depend on the type of interaction between the nodes. The authors considered two-dimensional cases of oscillations in one of the close-packed planes and three-dimensional cases when the motions of atoms have three components in space for a tungsten cell consisting of 2000 atoms and 31.6×31.6×31.6 Å in size. The amplitude-frequency characteristics of these modes were calculated for several interatomic potentials available in the LAMMPS library. The study identified that several interatomic potentials, namely eam.fs, set, Olsson, and Zhou show practically identical results, which is an indirect confirmation of their validity and the possibility of their use for modeling extreme impacts in the considered lattice. The authors calculated such characteristics of the system as kinetic energy, heat capacity, and pressure. Based on the results obtained, one can assume that mode 15, due to the modulation instability, will lead to the energy localization on individual atoms.