We present an accurate and efficient method for calculating highly excited 3D van der Waals (vdW) vibrational states of structurally nonrigid M · R complexes, between an atom R and a large, arbitrarily shaped molecule M. Our method combines the atom-molecule Hamiltonian of Brocks and van Koeven, in which Cartesian components of the vector connecting R and the center of mass of M are used as internal coordinates, with the 3D discrete variable representation (DVR) of all three intermolecular large amplitude degrees of freedom. Our 3D DVR method is aimed at highly anisotropic M · R complexes, in which the size of the molecule is typically larger than the average atom-molecule distance. The symmetry of the complex (if any) is exploited by constructing symmetry adapted 3D DVRs which transform under the irreducible representations of the symmetry group, and bring the Hamiltonian matrix to a block diagonal form. The 3D DVR is particularly well suited for description of excited and strongly coupled, delocalized vdW states, and internal motions on very anharmonic intermolecular potentials with multiple minima. We use this method to calculate vdW vibrational energy levels and wave functions of a floppy complex naphthalene · Ar. The lower-lying vdW states are assigned by inspection of the wave function plots.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry