Application of a new ensemble conserving quantum dynamics simulation algorithm to liquid para-hydrogen and ortho-deuterium

Abstract

We apply the Feynman-Kleinert Quasi-Classical Wigner (FK-QCW) method developed in our previous work [Smith et al., J. Chem. Phys. 142, 244112 (2015)] for the determination of the dynamic structure factor of liquid para-hydrogen and ortho-deuterium at state points of (T = 20.0 K, n = 21.24 nm(-3)) and (T = 23.0 K, n = 24.61 nm(-3)), respectively. When applied to this challenging system, it is shown that this new FK-QCW method consistently reproduces the experimental dynamic structure factor reported by Smith et al. [J. Chem. Phys. 140, 034501 (2014)] for all momentum transfers considered. This shows that FK-QCW provides a substantial improvement over the Feynman-Kleinert linearized path-integral method, in which purely classical dynamics are used. Furthermore, for small momentum transfers, it is shown that FK-QCW provides nearly the same results as ring-polymer molecular dynamics (RPMD), thus suggesting that FK-QCW provides a potentially more appealing algorithm than RPMD since it is not formally limited to correlation functions involving linear operators.

On static triplet structures in fluids with quantum behavior

“…The interparticle potential for liquid para-H 2 is the Silvera-Goldman potential (SG3) including three-body contributions, 68 which is a standard choice for studies of this system. Note that SG3 is a one-center potential suited for the range of conditions dealt with in this work, 58,[69][70][71][72][73][74] and the computed structures correspond to correlations involving whole para-H 2 molecules. (For the increasing importance of anisotropic effects in liquid hydrogen for densities ≥0.037 Å 3 , see Refs.…”

A new class of ensemble conserving algorithms for approximate quantum dynamics: Theoretical formulation and model problems

“…Furthermore, the practical application of these two new methods to realistic condensed phase systems is not out of reach since they present only a minimum amount of additional computational load as compared to FK-LPI. This potential will be realized in a forthcoming paper 26 in which we present the multidimensional generalization of these dynamics and apply FK-QCW(2) for the determination of the dynamic structure factor in low temperature liquid para-hydrogen and ortho-deuterium and compare the results with those presented in Ref. 19.…”

Path-integral approximations to quantum dynamics

“…In Refs. [127][128][129], a planetary model was developed, which does capture the fluctuation dynamics to within a local harmonic approximation. This model gave good results for the dynamic structure factor of liquid hydrogen [128], and good overall predictions of the spectrum of liquid water [129], but it is too approximate to be used, for example, to investigate how nonlinearity in the dipole-moment surface of water affects the lineshapes.…”