Molecular correlation energy with the HF–CC method

The `HF-CCʹ model is extended from atomic to molecular systems. An analysis of the total and binding energy components points out mechanisms of molecular binding and a strategy to compute the latter via a partitioning of the correlation energy into atomic and molecular components. The HF-CC model is size consistent and basis set independent. We considered 41 molecules at optimised geometry with basis sets near to the Hartree–Fock limit. The average atomisation energy is 69.65% of the experimental data (average error is 147.59 kcal/mol) from Hartree–Fock and becomes 95.10%, 97.68%, and 99.52% (average errors become 31.79 kcal/mol, 10.54 kcal/mol, and 2.36 kcal/mol, respectively) for the HF-CC model with either one parameter (for the H atom), or one parameter per each atomic species, or one parameter per each class of an atomic species; the Becke–Perdue BP-86 density functional yields 94.45% with an average error of 20.43 kcal/mol.