Revision and extension of the HF-CC method

Abstract

The Hartree–Fock-correlation correction (HF-CC) molecular model is a recent post-HF perturbation model which decomposes the correlation correction into atomic and molecular components. In this work, the HF-CC model is modified with attention to weak and very weak interactions, and validated by computing the atomisation energy of 112 test molecules: 104 closed shell, from diatomic to naphthalene, and 8 radicals. The atomisation energies, computed at six successive approximations by optimising an increasing number of empirical parameters have mean deviations of 13.82, 11.90, 6.32, 4.57, 0.54 and 0.05kcal/mol, respectively, relative to experiments. The method is successfully extended to weak interactions testing the dimer and trimer of water and the complexes H2O–X with X=Li+, Na+, K+, F−, Cl−. The feasibility to predict very weak interactions is tested with computations of van der Waals energies: at the computed minimum. He2, Ne2 and Ar2 have inter nuclear distances and interaction energies in agreement with laboratory data. Finally, the total molecular binding energy is decomposed into computed bond energies that are comparable to the available experimental bond energies.