A quantum Monte Carlo study of systems with effective core potentials and node nonlinearities

Abstract

We study beryllium dihydride (BeH${}_2$) and acetylene (C${}_2$H${}_2$) molecules using real-space diffusion Monte Carlo (DMC) method. The molecules serve as perhaps the simplest prototypes that illustrate the difficulties with biases in the fixed-node DMC calculations that might appear with the use of effective core potentials (ECPs) or other nonlocal operators. This is especially relevant for the recently introduced correlation consistent ECPs (ccECPs) for $2s2p$ elements. Corresponding ccECPs exhibit deeper potential functions due to higher fidelity to all-electron counterparts, which could lead to larger local energy fluctuations. We point out that the difficulties stem from issues that are straightforward to address by upgrades of basis sets, use of T-moves for nonlocal terms, inclusion of a few configurations into the trial function and similar. The resulting accuracy corresponds to the ccECP target (chemical accuracy) and it is in consistent agreement with independent correlated calculations. Further possibilities for upgrading the reliability of the DMC algorithm and considerations for better adapted and more robust Jastrow factors are discussed as well.

13 pages, 5 figures

References in corpus (11)

• Beyond the locality approximation in the standard diffusion Monte Carlo method
• Applications of quantum Monte Carlo methods in condensed systems
• Interactions between Large Molecules: Puzzle for Reference Quantum-Mechanical Methods
• QMCPACK: Advances in the development, efficiency, and application of auxiliary field and real-space variational and diffusion Quantum Monte Carlo
• A New Generation of Effective Core Potentials for Correlated Calculations
• Spectroscopic accuracy directly from quantum chemistry: application to ground and excited states of beryllium dimer
• Shape and Energy Consistent Pseudopotentials for Correlated Electron systems
• A first-principles Quantum Monte Carlo study of two-dimensional (2D) GaSe
• Water on BN doped benzene: A hard test for exchange-correlation functionals and the impact of exact exchange on weak binding
• Nonlocal pseudopotentials and time-step errors in diffusion Monte Carlo
• Weighted nodal domain averages of eigenstates for quantum Monte Carlo and beyond