ИСТИНА

Various approaches are used to find the true bound eigenstates and corresponding eigenfunctions for Van der Waals complexes [1]. Coupled channel method handles the radial coordinate by direct numerical propagation on a grid, whereas other coordinates are accounted for using a basis set. Calculations that use an exact formulation, with no approximation other than basis set truncation, usually referred to as closecoupling calculations, are notoriously computationally expensive. In case of Van der Waals complexes, the most important approximation is the helicity decoupling approximation, which neglects off-diagonal terms of the Coriolis coupling operator. The present paper aims at quantifying how the diagonal and off-diagonal Coriolis terms affect the calculated eigenvalues, taking Ar-HCl dimer as an example. We have used the Johnson renormalized propagator [2] in the calculation that fully disregards Coriolis interaction. The calculations employing both close-coupling and helicity decoupling formulations were done using the recent release of BOUND program [3]. The structure of rovibrational levels is correctly represented in helicity decoupling approximation, except for subtle rotational effects, such as parity splitting. Subsequent analysis in the framework of degenerate perturbation theory is undertaken to reproduce the fine structure of eigenvalues. The properties of the perturbation series are discussed, and the results based on perturbation corrections are compared with accurate close-coupling eigenvalues. The classical partition function is calculated based on the recently developed approach [4]. The correspondence between state-by-state quantum and classical partition functions is discussed. This work was partially supported by RFBR and RFBR-CNRS Grants in the frame of 18-05-00119, 18-32-20156, 18-55-16006 projects. References: 1. J.M. Hutson, Comput. Phys. Commun. 84, 1–18 (1994). 2. B.R. Johnson, J. Chem. Phys. 69, 4678–4688 (1978). 3. J.M. Hutson, and C. Sueur. arXiv preprint 1811.09111 (2018). 4. N. Chistikov, A.A. Finenko, S.E. Lokshtanov, S.V. Petrov, A.A.Vigasin, J. Chem. Phys. 149, 194304 (2018).