A correlation-relaxation-balanced direct method at the second order perturbation theory for accurate ionization potential predictions

The development of a quasi-particle approach for an accurate yet efficient prediction of a complete ionization potential (IP) spectrum, from valence down to core electrons for the system of interest, is a long-cherished goal in quantum chemistry. Based on the physical understanding of the electron correlation and relaxation effects at the second order perturbation theory, we present here a correlation-relaxation-balanced direct method, dubbed CRB-MP2, via a parameter scaled scheme of the 2 ph (two-particle, one-hole summation) and 2 hp (two-hole, one-particle summation) terms. With almost no extra computational cost after a normal MP2 procedure, the CRB-MP2 method yields high quality valence and core IPs for a wide range of species. A direct approach for complete IP spectrum calculations with both computational accuracy and efficiency is therefore established. With almost no extra computational cost after a normal MP2 procedure, the CRB-MP2 method proposed here yields high quality valence and core IPs for a wide range of species.