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Bound and quasi‐bound states of the LiFH van der Waals molecule
Author(s) -
Burcl R.,
Piecuch P.,
Špirko V.,
Bludský O.
Publication year - 2000
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/1097-461x(2000)80:4/5<916::aid-qua41>3.0.co;2-v
Subject(s) - van der waals force , chemistry , ab initio , basis set , triatomic molecule , bound state , potential energy surface , ab initio quantum chemistry methods , coupled cluster , atomic physics , van der waals strain , hamiltonian (control theory) , potential energy , van der waals radius , physics , molecule , computational chemistry , quantum mechanics , density functional theory , mathematical optimization , mathematics , organic chemistry
The fully dimensional potential energy surface of the ground electronic state of the LiFH van der Waals complex was constructed by fitting ab initio energies obtained on a grid of ca. 2000 nuclear geometries. The ab initio calculations were performed using the coupled‐cluster approach with single, double, and noniterative perturbative triple excitations [the CCSD(T) method]. The large and carefully optimized basis set, consisting of 140 orbitals, was employed. All CCSD(T) energies were corrected for the effects of the basis set superposition error and deformation of the HF monomer in the LiFH complex. The basis set superposition error‐corrected CCSD(T) potential energy surface is characterized by a relatively deep, 1991 cm −1 , van der Waals well and a late barrier for the Li+HF→LiF+H reaction located at 2017 cm −1 above the Li+HF asymptote. The LiFH complex is bent (the LiFH angle is 109°). The bending LiFH angle characterizing the saddle point is 71°. The fitted potential energy surface was used to calculate the bound and low‐lying quasi‐bound vibrational states of the LiFH complex. The required ro‐vibrational calculations were performed within the framework of the Sutcliffe–Tennyson Hamiltonian for triatomic molecules. The energy positions and widths of the quasi‐bound states were obtained using the stabilization method. The ro‐vibrational problem was solved both variationally, by diagonalizing the Hamiltonian matrix in a discrete basis set, and by using the perturbative approach based on the adiabatic separation of vibrational motions. All spectroscopic information obtained in this study was rationalized in terms of effective potentials for the van der Waals stretch and bend motions arising from the adiabatic separation of the high‐ and low‐frequency modes. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 916–933, 2000