quantum Monte Carlo noncovalent interactions

While it is empirically accepted that the fixed-node diffusion Monte-Carlo (FN-DMC) depends only weakly on the size (beyond a certain reasonable level) of the one-particle basis sets used to expand its guiding functions, limits of this observation are not settled yet. Our recent work indicates that under the FN error cancellation conditions, augmented triple zeta basis sets are sufficient to achieve high-quality benchmark single-point energy differences in a number of small noncovalent complexes. In this preliminary progress report, we report on a possibility of significant truncation of the one-particle basis sets used to express the FN-DMC guiding functions, that has no visible effect on the accuracy of the production energy differences. The proposed scheme shows only modest increase of the local energy variance, indicating that the total CPU cost of large-scale benchmark noncovalent interaction energy FN-DMC calculations employing Gaussians may be reduced.