Quantum Monte Carlo Calculation of Atoms and Molecules

Michel Caffarel, Carlo, UK +2 more

Myung Won Lee, Massimo Mella, Andrew M. Rappe

We calculated the energies and atomic forces of first-row monohydrides, carbon monoxide, and small organic polyatomic molecules using quantum Monte Carlo (QMC) method. Accurate forces were obtained with the method of Casalegno, Mella, and Rappe, combining the Hellmann- Feynman theorem forces calculated by the Assaraf-Caffarel method with a many-body Pulay correction. Improved algorithms for the minimization of the variational integral were useful in the force calculations.

Myung Won Lee, Sergey V. Levchenko, Andrew M. Rappe

We calculated the variational and diffusion quantum Monte Carlo forces using the Hellmann–Feynman theorem and Pulay's correction for the first-row diatomic and triatomic molecules (CO, NO, CO2 and NO2). It is demonstrated that Pulay's correction is important for accurate calculation of forces on non-hydrogen atoms.

Dmitry Yu. Zubarev, Brian M. Austin, William A. Lester

Jonas Feldt, Roland Assaraf

We propose a method to remove the large statistical fluctuations coming from the core regions when applying an all-electron Variational Monte Carlo method to a molecule. It is based on an efficient subsampling approach which performs sidewalks in these regions. The gain in variance is displayed for a series of atoms and we show that this gain is transferable to molecules on alkane chains and clusters of silicon. For these systems the gain in numerical efficiency is presented, and can be extrapolated to ∼ 22 and ∼ 420 for larger systems when computing the variational energy with a Slater determinant. These results are a proof of concept for numerically affordable all-electron quantum Monte Carlo calculations on molecules with large atomic charges.