Transport properties of liquid para-hydrogen: The path integral centroid molecular dynamics approach

Abstract

Several fundamental transport properties of a quantum liquid para-hydrogen (p-H2) at 17 K have been numerically evaluated by means of the quantum dynamics simulation called the path integral centroid molecular dynamics (CMD). For comparison, classical molecular dynamics (MD) simulations have also been performed under the same condition. In accordance with the previous path integral simulations, the calculated static properties of the liquid agree well with the experimental results. For the diffusion coefficient, thermal conductivity, and shear viscosity, the CMD predicts the values closer to the experimental ones though the classical MD results are far from the reality. The agreement of the CMD result with the experimental one is especially good for the shear viscosity with the difference less than 5%. The calculated diffusion coefficient and the thermal conductivity agree with the experimental values at least in the same order. We predict that the ratio of bulk viscosity to shear viscosity for liquid p-H2 is much larger than classical van der Waals simple liquids such as rare gas liquids.

Communication: Quantum molecular dynamics simulation of liquid para-hydrogen by nuclear and electron wave packet approach

“…1(a) and 1(b) indicates that the peaks and valleys of the RDF become broader and deviate toward the larger distance at the higher temperature, while the position of the first peak does not change, in agreement with the previous CMD results. 3,4,6 In addition, the shoulder of the first RDF peak is weakened at the higher temperature, reflecting the less structured p-H 2 liquid. The direct comparisons with the PIMC results are also given in Fig.…”

“…The deviation around the first peak is mainly attributed to the appearance of the shoulder in the NEWPMD; in fact, the deviation is larger at 14 K than at 25 K. It is well known that the RDF obtained from the classical MD exhibits a much sharper and thus an entirely different distribution, implying that the classical liquid is more likely to be solidified compared with the quantum liquid. 4 The current quantization of the hydrogen nuclei introduced by the NEW-PMD makes the intermolecular distance larger and makes the radial distribution much broader. The effective intermolecular attraction is reduced by the additional excluded volume effect and repulsive force caused by the hydrogen NWPs just as the liquid water case reported before.…”

“…Methods suitable for numerical simulations of real p-H 2 ensembles have been proposed using the path integral Monte Carlo (PIMC), 1, 2 linearized semiclassical initial value representation (LSC-IVR), 7,8 centroid molecular dynamics (CMD), 3,4,6 ring-polymer molecular dynamics (RPMD), 9 and the thermal Gaussian molecular dynamics (TGMD). 10 These all are based on the imaginary-time path-integral theory, and the latter four have been implemented for calculations of time correlation functions (TCFs) accounting for particularly important NQEs such as zero-point energy (ZPE) effect.…”

“…Due to the strong nuclear quantum effect (NQE), liquid p-H 2 shows broad radial distribution functions (RDFs) and rapid diffusion properties even at low temperature, which cannot be reproduced by the classical simulation approaches. [1][2][3][4][5][6] Hydrogen is of primary importance not only in the fundamental condensed phase physics but also in its potential applications as energy source without harmful byproducts. It is therefore important to establish an a priori computational method to predict the anomalous properties of p-H 2 liquids.…”

How to remove the spurious resonances from ring polymer molecular dynamics

“…7,8 They are especially useful for calculating diffusion coefficients and other transport properties of liquids, [9][10][11][12][13][14][15][16][17][18][19][20] and for including zero-point energy and tunnelling effects in the calculation of chemical reaction rates. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In these contexts, both methods appear to be reasonably reliable, on the basis of comparisons with full quantum mechanical results in cases where these are available, [25][26][27]29,30,33 and exact quantum mechanical moment constraints in cases where they are not.…”