Variational Reduced-density-matrix Method: Application to Nuclear Motion

The present work describes the development and generalization of variational reduced-density-matrix (RDM) theory. Building on previous advances in electronic RDM theory, a general method for the treatment of systems of mixed particles with more than two-body interactions is developed. A focus of this work is the application of the general theory to the problem of interacting nuclei and to the study of vibrational motion in atomic clusters and molecular systems. The approach developed here can be uniformly applied to classical geometry optimization, quantum systems described by empirical or semi-empirical potentials, and fully quantum molecular systems. A goal of these calculations is to develop a novel and consistent way for studying nuclear motion.