First-row hydrides: Dissociation and ground state energies using quantum Monte Carlo

Abstract

Accurate ground state energies comparable to or better than the best previous ab initio results can be obtained using the fixed-node quantum Monte Carlo (FN-DQMC) method. The residual energy, the nodal error due to the error in the nodal structure of a trial wave function, is examined in this study using nodal surfaces given by near HF-limit wave functions. The study is aimed at better understanding of the nodal error and the cancellation of nodal errors in calculating energy differences. Calculations have been carried out for the first-row hydrides LiH to FH and the corresponding atoms. The FN-DQMC ground state energies are among the lowest to date. The dissociation energies De have been calculated with accuracies of 0.5 kcal mol−1 or better. For all hydrides, the dissociation energies are consistent with experimental values. The fixed-node quantum Monte Carlo method can therefore offer a very straight-forward way to calculate highly accurate dissociation energies.