Quantum Monte Carlo and Related Approaches

The use of quantum Monte Carlo (QMC) to solve the electronic Schrödinger equation for atoms and molecules, an area that historically has been labeled ab initio quantum chemistry, is discussed. Discussion of alternative QMC techniques focuses on their conceptual foundations and their advantages and challenges relative to variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC). Fahy et al. studied the use of electron-nucleus terms in the correlation function that is used to readjust the electron density without reoptimizing molecular orbitals. Manten and Luchow (ML) created a linear scaling algorithm for evaluating the two-body terms in the Boys and Handy (BH) expansion. A series of papers by Badinski and co-workers have made significant andvances toward evalulating the Pulay terms in the expressions for the forces for systems with nonlocal pseudopotentials in DMC including accurate estimates for nodal terms and force estimates that use zero-variance properties to improve statistical efficiency.