All-dimensional H2–CO potential: Validation with fully quantum second virial coefficients

Abstract

We use a new high-accuracy all-dimensional potential to compute the cross second virial coefficient B12(T) between molecular hydrogen and carbon monoxide. The path-integral method is used to fully account for quantum effects. Values are calculated from 10 K to 2000 K and the uncertainty of the potential is propagated into uncertainties of B12. Our calculated B12(T) are in excellent agreement with most of the limited experimental data available, but cover a much wider range of temperatures and have lower uncertainties. Similar to recently reported findings from scattering calculations, we find that the reduced-dimensionality potential obtained by averaging over the rovibrational motion of the monomers gives results that are a good approximation to those obtained when flexibility is fully taken into account. Also, the four-dimensional approximation with monomers taken at their vibrationally averaged bond lengths works well. This finding is important, since full-dimensional potentials are difficult to develop even for triatomic monomers and are not currently possible to obtain for larger molecules. Likewise, most types of accurate quantum mechanical calculations, e.g., spectral or scattering, are severely limited in the number of dimensions that can be handled.

Evidence of Nonrigidity Effects in the Description of Low-Energy Anisotropic Molecular Collisions of Hydrogen Molecules with Excited Metastable Helium Atoms

“…It has been demonstrated that the vibrationally averaged surfaces perform better than the rigid-monomer ones also in predictions of other physical properties, like rovibrational spectra 13 − 15 , 38 , 39 or virial coefficients. 40 , 41 A main drawback of such an approximation is that, in principle, to obtain the vibrationally averaged surface one has to know the corresponding full-dimensional one. To avoid construction of a full-dimensional surface and minimize the number of geometries for which ab initio calculations have to be performed, we use the method developed in ref ( 42 ).…”

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

“…15 Full quantum treatment is needed to describe such motions, and the same is true for description of scattering of H 2 on CO. 16 The mixed second virial coefficient was calculated for this system using the path-integral Monte Carlo (PIMC) method. 17 The quantum approach has to be used for essentially all temperatures of interest; only above 1000 K can one rely on the classical values.…”

“…The current information on monomer-flexibility effects is limited. For the second virial coefficient of H 2 , Garberoglio et al 54 found that a rigid-monomer model with the bond length at its vibrationally averaged ground-state value gives results nearly identical to the fully flexiblemonomer calculation, and later effects of similar size (0.8% effect at 300 K and 0.09% at 1000 K) were found for H 2 -CO. 17 On the other hand, for H 2 O, it has been claimed that monomer flexibility has a large effect on B ( T ). Refson et al 55 computed this effect as 10% in the range 373–673 K, while Donchev et al 56 computed it as 20–40% for T ∊ 300 − 800 K, with 40% effect at 300 K. In contrast, recent calculations by Jankowski et al 21 gave much smaller monomer flexibility effects.…”

Stereodynamic control of cold rotationally inelastic CO + HD collisions

“…For the PES we used the recent high-accuracy 6D CO+H 2 potential reported by Faure et al [60,61]. This potential was chosen as it reproduces the proper physical inverse-power dependence with the intermolecular distance, R, at long range which is crucial for low energy collisions.…”