diatom_scan calculation style

Lucas M. Hale, lucas.hale@nist.gov, Materials Science and Engineering Division, NIST.

Introduction

The diatom_scan calculation style evaluates the interaction energy between two atoms at varying distances. This provides a measure of the isolated pair interaction of two atoms providing insights into the strengths of the attraction/repulsion and the effective range of interatomic spacings. This scan also gives insight into the computational smoothness of the potential’s functional form.

Version notes

  • 2019-07-30: Notebook added.

  • 2020-05-22: Version 0.10 update - potentials now loaded from database.

  • 2020-09-22: Setup and parameter definition streamlined. Method and theory expanded.

  • 2022-02-16: Notebook updated to reflect version 0.11.

Additional dependencies

Disclaimers

  • NIST disclaimers

  • No 3+ body interactions are explored with this calculation as only two atoms are used.

Method and Theory

Two atoms are placed in an otherwise empty system. The total energy of the system is evaluated for different interatomic spacings. This provides a means of evaluating the pair interaction component of an interatomic potential, which is useful for a variety of reasons

  • The diatom_scan is a simple calculation that can be used to fingerprint a given interaction. This can be used to help determine if two different implementations produce the same resulting potential when direct comparisons of the potential parameters is not feasible.

  • For a potential to be suitable for radiation studies, the extreme close-range interaction energies must be prohibitively repulsive while not being so large that the resulting force on the atoms will eject them from the system during integration. The diatom_scan results provide a means of evaluating the close-range interactions.

  • The smoothness of the potential is also reflected in the diatom_scan energy results. Numerical derivatives of the measured points can determine the order of smoothness as well as the approximate r values where discontinuities occur.

  • Evaluating large separation values provides a means of identifying the energy of the isolated atoms, given that the separation exceeds the potential’s cutoff. The isolated_atom calculation is an alternative method for obtaining this.