Exploiting locality in FCIQMC for fast excitation generation

Abstract

In this paper we propose an improved excitation generation algorithm for the full configuration interaction quantum monte carlo (FCIQMC) method, which is particularly effective in systems described by localized orbitals. The method is an extension of the precomputed heat-bath (PCHB) strategy of Holmes et al., with more effective sampling of double excitations and a novel approach for non-uniform sampling of single excitations. We demonstrate the effectiveness of the algorithm for a chain of 30 hydrogen atoms with atom-localized orbitals, a stack of benzene molecules, an Fe-porphyrin model complex, whereby we show an overall efficiency gain by a factor of two to four, as measured by variance reduction per wall-clock time.