An ab initio study of intermolecular interaction of hydrogen fluoride tetramer

Possible HF tetramer geometries have been optimized employing the density functional B3LYP method and the aug-cc-pVQZ basis set. Deformation energy has been calculated at the B3LYP/aug-cc-pVQZ level. After the BSSE correction with the CP method, two-body intermolecular interaction energy, three-body nonadditive intermolecular interaction energy, and four-body nonadditive intermolecular interaction energy (ΔE_c[4]) have been obtained at the levels of B3LYP/aug-cc-pVQZ, B3LYP/aug-cc-pVTZ//B3LYP/aug-cc-pVQZ, and MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVQZ. Calculated results show that the three-body nonadditive intermolecular interaction energy is important for the optimized structures of HF tetramer. At the MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVQZ level, the four-body nonadditive intermolecular interaction strength arrives at -4.5 kJ/mol in the optimized eight-membered ring structure, but is extremely weak in other optimized structures. The comparison between MP2 and B3LYP calculated intermolecular interaction energies shows that the B3LYP method is applicable to the calculation of the intermolecular interaction energy of HF tetramer when the basis set reaches augcc-pVTZ. ΔE_c[4] occupies 8-32% of the total intermolecular interaction energy when the intermolecular distances of the eight-membered ring structure are in the range of 1.06-1.37 Å.