R12-calibrated H2O–H2 interaction: Full dimensional and vibrationally averaged potential energy surfaces

Abstract

The potential energy surface of H(2)O-H(2) is of great importance for quantum chemistry as a test case for H(2)O-molecule interactions. It is also required for a detailed understanding of important astrophysical processes, namely, the collisional excitation of water, including the pumping of water masers and the formation of molecular hydrogen on icy interstellar dust grains. We have calculated the interaction for H(2)O-H(2) by performing both rigid-rotor (five-dimensional) and non-rigid-rotor (nine-dimensional) calculations using the coupled-cluster theory at the level of singles and doubles with perturbative corrections for triple excitations [CCSD(T)] with moderately large but thoroughly selected basis set. The resulting surface was further calibrated using high precision explicitly correlated CCSD(T)-R12 calculations on a subset of the rigid-rotor intermolecular geometries. The vibrationally averaged potential is presented in some details and is compared with the most recent rigid-rotor calculations. We explain, in particular, as to why vibrationally averaged rigid-rotor geometries are a better choice than equilibrium geometries. Our fit of the vibrationally averaged surface provides for the first time an accuracy of approximately 3 cm(-1) in the van der Waals minimum region of the interaction. The overall accuracy of the nine-dimensional surface and fit is lower but remains of the order of 3%-4% of the anisotropy in the domain spanned by the vibrational functions.

Overtone vibrational spectroscopy in H2-H2O complexes: A combined high level theoretical ab initio, dynamical and experimental study

“…A potential energy surface (PES) for H 2 -H 2 O that includes all nine internal degrees of freedom has been calculated ab initio by Valiron et al 1,47 with the use of the CCSD(T)-R12 method (coupled-cluster with singles, doubles, and perturbative triples, explicitly correlated). This PES is independent of nuclear mass and can be employed for any of the water-hydrogen isotopologues.…”

“…As a result this complex offers an unprecedented opportunity for a purely "first principles" test between experiment (i.e., high resolution spectroscopy) and theory (ab initio/dynamics calculations). Indeed, the small electron number has already stimulated the development of a high level ab initio potential energy surface 1 (Fig. 1).…”

“…24,26,[28][29][30] The need for high level predictive understanding for such high pressure/temperature combustion phenomena is clearly important, which in turn depends pivotally on benchmark accuracy of the full 9D potential H 2 + H 2 O energy surface. 1,15,17,[20][21][22][23] Of particular interest in the interstellar medium (ISM) is the corresponding weakly bound complex, H 2 -H 2 O, due in part to predominance of atomic and molecular hydrogen in the universe. 31 Indeed, certain regions of the ISM depleted in deep ultraviolet radiation tend to have appreciable concentrations of H 2 molecules rather than H atoms, 32 which can in fact trigger chemical synthesis into higher molecular weight species.…”

“…The current work focuses on spectroscopy, dynamics, and interaction potentials for H 2 + H 2 O, 1,13,[15][16][17][18][19][20][21] which proves to be relevant in a wide range of terrestrial and extraterrestrial venues. 2,[22][23][24][25][26] In high temperature H 2 /O 2 combustion, for example, collisions of the highly energized product H 2 O molecules with H 2 reactant provide an important mechanism for heat flow as well as establishing local thermodynamic equilibrium in the flames.…”

Potential generation and path‐integral Monte Carlo in study of microscopic superfluidity

“…For larger systems, for example, HCCCNAHe, [52] OCSAHe, [53,54] and OCSAH 2 , [55] less expensive many-body perturbation theory at the nth order [56] with n5224 can also be used. If higher accuracy is pursued, for example, H 2 OAH 2 , [57] methods that include explicit correlation, for example, CCSD(T)-R12, [58,59] can be used. A combined CCSD(T)/SAPT scheme was used to generate the potential for the HCOOCH 3 -He dimer.…”