Efficient and Accurate Modeling of Quantum Nuclear Effects in Molecules and Materials

Nuclear quantum effects (NQE), which includes both zero-point motion and tunneling, exhibits an important influence on equilibrium and dynamical properties of molecules and materials. These effects can be taken into account using the Feynman-Kac imaginary-time path integral molecular dynamics (PIMD) calculations. Efficient PIMD schemes require the knowledge about high-order derivatives of the potential energy, which limits their practical applicability in ab initio simulations. Recently it was shown [V. Kapil et al., J. Chem. Phys. (2016)] that the finite differences method can be successfully employed to compute these derivatives, considerably decreasing the computational costs of ab initio PIMD simulations. Here we demonstrate how the efficiency of such simulations can be further improved by combining PIMD approach and thermodynamic perturbation theory [I. Poltavsky and A. Tkatchenko, Chem. Sci. (2016)]. The developed method allows the calculation of NQE in realistic molecules and materials, and paves the way to converged PIMD simulations even at relatively low temperature.