Davidson correction

The Davidson correction is an energy correction often applied in calculations using the method of truncated configuration interaction, which is one of several post-Hartree–Fock ab initio quantum chemistry methods in the field of computational chemistry. It was introduced by Ernest R. Davidson.The Davidson correction is very popular due to its low computational cost. The correction improves the contribution of electron correlation to the energy. The size-consistency and size-extensivity problems of truncated CI are alleviated but still exist. In small molecules, accuracy of the corrected energies can be similar to results from coupled cluster theory calculations.Davidson correction improves both size consistency and size extensivity of CISD energies. Therefore, Davidson correction is frequently referred to in literature as size-consistency correction or size-extensivity correction.Similar corrections exist for MR-CISD energies, including multi-reference Davidson correction, Pople correction, and others. These methods can be used to correct excited state energies.