How Important is Orbital Choice in Single-Determinant Diffusion Quantum Monte Carlo Calculations?

摘要

The accuracy of total electronic energies obtained using the fixed-node diffusion quantum Monte Carlo (FN-DMC) method is determined by the choice of the many-body nodal surface. Here, we perform a systematic comparison of the quality of FN-DMC energies for a selection of atoms and diatomic molecules using nodal surfaces defined by single determinants of Hartree—Fock, B3LYP, and LDA orbitals. Through comparison with experimental results, we show that the use of Kohn— Sham orbitals results in significandy improved FN-DMC atomization energies over those obtained using Hartree—Fock orbitals. We also discuss the effect of spin contamination in the orbitals.