Diatomics-in-ionic-systems and ab initio predictions for the stationary points on potential energy surfaces of the (HF)n clusters (n=3-6)

Predictions of the diatomics-in-ionic-systems model for the variety of stationary points on the potential energy surfaces of the hydrogen fluoride clusters (HF)(n) (3 less than or equal to n less than or equal to 6) are compared to the results of ab initio MP2/6-311+G(2d,2p) calculations as well as to the results of the polarizable mechanics model of Hodges [J. Phys. Chem. A 102, 2455 (1998)]. The diatomics-in-ionic-systems scheme which relies on the balanced treatment of neutral and ionic contributions to the electronic properties of polyatomic species within the diatomics-in-molecules theory takes into account here the mixing of the FH and F-H+ electronic states. The corresponding mixing coefficient serves as a single principal adjustable parameter of the model, finally selected by the reference value of the binding energy of (HF)(3). It is shown that structures and energies of the main cyclic isomers are in a good agreement with the best estimates of Quack and Suhm [Conceptual Perspectives in Quantum Chemistry (Kluwer, Dordrecht, 1997)]. Every prediction of this model for the stationary points corresponding to 16 higher energy structures of (HF)(n) is confirmed by the MP2 ab initio data. (C) 1999 American Institute of Physics. [S0021-9606(99)30532-8].