Extending \textit{ab initio} plasma-surface simulations to experimentally relevant scales

TL;DR

This paper reviews methods to extend ab initio plasma-surface simulations to experimentally relevant scales, focusing on semi-classical molecular dynamics and strategies to bridge the gap in length and time scales.

Contribution

It summarizes theoretical approaches from surface physics to improve plasma-surface interaction simulations beyond current ab initio limitations.

Findings

Semi-classical MD simulations can approximate ab initio quality.

Current simulations are limited to very short timescales.

Various strategies exist to extend simulation scales without losing first-principles accuracy.

Abstract

The physical processes at the interface of a low-temperature plasma and a solid are extremely complex. They involve a huge number of elementary processes in the plasma, in the solid as well as charge, momentum and energy transfer across the interface. In the majority of plasma simulations these surface processes are either neglected or treated via phenomenological parameters. However, those parameters are known only in some cases, so such an approach is very inaccurate and does not have predictive capability. Therefore, improvements are highly needed. In this paper we briefly summarize relevant theoretical methods from solid state and surface physics that are able to contribute to an improved simulation of plasma-surface interaction in the near future. Full \textit{ab initio} quantum simulations are feasible only for extremely short times and/or small system sizes. A substantial simplification is achieved when electronic quantum effects are not treated explicitly. Then one arrives at semi-classical molecular dynamics (MD) simulations for the heavy particles that have become the main workhorse in surface science simulations. Using microscopically founded potentials and force fields as an input, these MD simulations approach the quality of \textit{ab initio} simulations, in many cases. However, despite their simplified nature, these simulations require a time step that is of the order or below one femtosecond making it prohibitive to reach experimentally relevant scales of minutes. To bridge this gap in length and time scales without compromising the first principles character of the simulations, many physical and computational strategies have been put forward in surface science. This paper presents a brief overview on different methods and their underlying physical ideas, and we compare their strengths and weaknesses.