The first and second terms are ESP contributions from the monomers and dimers in protein A or B, respectively, and the third term is the ESP associated with the atomic nuclei in protein A or B. The fourth term is a two-body correction from the dimers formed by proteins A and B, which is halved and added to the pESP. Notably, a simple sum of the pESPs of proteins A (equation (6)) and B (equation (7)) is exactly equivalent to the total ESP of the complex (equation (5)):