Space warp coordinate transformation for efficient ionic force calculations in quantum Monte Carlo*

Although ab-initio quantum Monte Carlo (QMC) ground-state energy calculation is standard and widely used in physics and chemistry, calculation of atomic forces is still under technical/algorithmic development. We have benchmarked the accuracy of all-electron variational Monte Carlo (VMC) and lattice regularized diffusion Monte Carlo (LRDMC) forces for various mono- and hetero-nuclear dimers. The VMC and LRDMC forces were calculated with the so-called space warp coordinate transformation (SWCT) and appropriate regularization techniques to remove the infinite variance problem. We have found that the appropriate use of the SWCT transformation makes the calculation of forces very efficient and feasible also for large atomic number. This is a quite promising conclusion from the viewpoint of the application of QMC forces, opening the door for future important applications of QMC in electronic structure calculations.