Calculation of the Transport and Relaxation Properties of the Ar···HCl van der Waals Complex Using a New Potential Energy Surface: Comparison of the Classical and Full Quantum Mechanical Kinetic Theory Results with Molecular Dynamics Simulations

The intermolecular potential energy surface (PES) of
the Ar···HCl
complex was calculated at the RCCSD(T)/aug-cc-pvQz-BF level of theory. The obtained potential was expanded in terms
of Legendre polynomials and fitted to a mathematical model. The fitting
results are highly correlated with the ab initio PES data with SD
= 5.9 × 10–3 cm–1 and average
absolute deviation (AAD) = 4.0 × 10–6 cm–1. The interaction second virial coefficients (B12) in the temperature range of 190–480
K were calculated by considering classical and first quantum corrections
and compared with the available experimental data. A reasonable agreement
with the experimental and calculated B12 was obtained. The PES was also used to obtain the rovibrational
energy levels, and the spectroscopic rovibrational constants were
obtained. It was found that the D0 values
differ ∼2.25 cm–1 from the experimental values
of the ground rovibrational state. Furthermore, the obtained potential
was used to calculate the transport and relaxation properties using
full quantum close-coupling (CC) formalism and the classical kinetic
theory methods based on the Mason–Monchik approximation (MMA).
It was found that the deviation between MMA and CC calculations is
increased with increasing the temperature due to the higher influence
of the rotational degrees of freedom on the transport properties.
Also, the contribution of the inelastic (off-diagonal) transitions
for diffusion coefficient is higher than the viscosity. Furthermore,
the classical molecular dynamics simulations were performed using
LJ(12,6) and Vashishta models, to calculate the interaction diffusion
and viscosity coefficients, and compared with the results of the full
quantum CC calculations. The obtained results confirm that the Vashishta
model is better fitted to the ab initio potentials and is more accurate
than LJ(12,6) in calculation of the diffusion coefficients.