Partitioning of molecular systems and subsystem replacement by single-centered perturbations: I. A partitioning theorem and the pseudo substituent technique

Abstract

Molecular systems are partitioned into subsystems. A general theorem is developed which relates the total molecular secular equation to the characteristic polynomials of these molecular subsystems. To selectively study subsystems of chemical interest, the linked substituents are approximated by a perturbing single-centered atomic-like substituent called a pseudo substituent. A criterion for replacement by pseudo substituent representations is developed. The transferability of pseudo substituent representations to different molecules facilitates complete molecular studies. A perturbing potential for the pseudo substituent replacement is proposed.