Fully quantum calculation of the second and third virial coefficients of water and its isotopologues fromab initiopotentials

Abstract

Path-integral Monte Carlo methods were applied to calculate the second, B(T), and the third, C(T), virial coefficients for water. A fully quantum approach and state-of-the-art flexible-monomer pair and three-body potentials were used. Flexible-monomer potentials allow calculations for any isotopologue; we performed calculations for both H2O and D2O. For B(T) of H2O, the quantum effect contributes 25% of the value at 300 K and is not entirely negligible even at 1000 K, in accordance with recent literature findings. The effect of monomer flexibility, while not as large as some claims in the literature, is significant compared to the experimental uncertainty. It is of opposite sign to the quantum effect, smaller in magnitude than the latter below 500 K, and varying from 1% at 300 K to 10% at 700 K. When monomer flexibility is accounted for, results from the CCpol-8sf pair potential are in excellent agreement with the available experimental data and provide reliable B(T) at temperatures outside the range of experimental data. The flexiblemonomer MB-pol pair potential yields B(T) that are slightly too high compared to experiment. For C(T), our calculations confirm earlier findings that the use of three-body potential is necessary for meaningful predictions. However, due to various uncertainties of the potentials used, especially the three-body ones, we were not able to establish benchmark values of C(T), although our results are in qualitative agreement with available experimental data. The quantum effect, never before included for water, reduces the magnitude of the classical value for H2O by a factor of 2.5 at 300 K and is not entirely negligible even at 1000 K.

A Reference Equation of State for Heavy Water

“…Both the new EOS and the previous EOS exhibit qualitatively correct low-temperature behavior, but the EOS of Hill et al 11 incorrectly produces negative B(T) at high temperatures. The new EOS is in excellent agreement with the recently established theoretical data of Garberoglio et al 112 throughout the temperature range, meaning that its vapor densities can be trusted even at temperatures where no experimental data exist. As discussed in Sec.…”

“…Because our EOS was extensively fitted to these densities, the virial-coefficient data were not considered additionally in the fit. Instead, the EOS was fitted to the theoretically obtained second virialcoefficient data of Garberoglio et al 112 These B(T) were calculated from a high-quality flexible pair potential 114 with full accounting for quantum effects, agreeing with the available experimental data for both D 2 O and H 2 O but covering a much wider temperature range. The B(T) data are depicted in the top panel of Fig.…”

“…The only experimental C(T) data for heavy water were again taken from Kell et al, 89 but their uncertainty was not stated. We also plot five points given by Garberoglio et al 112 which were based on high-quality pair 114 and threebody 115 potentials. Unlike with B(T), these theoretical C(T) values are not considered to be highly accurate.…”

Observation of the Low‐Frequency Spectrum of the Water Dimer as a Sensitive Test of the Water Dimer Potential and Dipole Moment Surfaces

“…Another one [26] follows the basic strategy used to develop the HBB2 potential. [28] In the low-temperature region the results from CCpol-8s/f and HBB2 are closer to each other and to experiment than are the results from MB-Pol. All of these dimer potentials give good agreement with experiment for VRT levels and tunneling splittings of (H 2 O) 2 and the six fundamental intramolecular bend and vibrational energies.…”

“…[24,26,27] Very recently,q uantum calculations of the second virial coefficient over the temperature range 300 to roughly 1200 K using HBB2, MB-Pol, and CCpol-8s/f were reported. [28] In the low-temperature region the results from CCpol-8s/f and HBB2 are closer to each other and to experiment than are the results from MB-Pol. At higher temperature all potentials give similar and accurate results.O verall the results using CCpol-8s/f are the most accurate ones.I ns ummary,t hese three flexible water dimer potentials appear to be highly accurate,a tl east for the properties examined to date.…”