Stochastic and deterministic crystal structure solution methods in GSAS-II: Monte Carlo/simulated annealing versus charge flipping

Abstract

Crystallographic studies frequently involve the determination of a previously unknown crystal structure; General Structure Analysis System (GSAS)-II provides two methods for this purpose. The Monte Carlo/simulated annealing method is fundamentally stochastic in nature; random trials are tested for suitability by comparing calculated structure factors with a suite of observed ones. In contrast, the charge flipping method may begin with a suite of random structure factor phases, but the subsequent mathematical steps are entirely deterministic even though they appear to display chaotic behavior. This paper will briefly describe these methods as implemented in GSAS-II, illustrating their use with examples.