Energy formalism of an X-ray electron density of large biological molecules

Lou Massa

Hunter College, Department of Chemistry,

The City University of New York, USA

lmassa@hunter.cuny.edu

Abstract: N-representability is a crucial concept that ensures a density matrix corresponds to an N-body antisymmetric wave function. This antisymmetry is the theoretical counterpart of the experimental principle of electron indistinguishability. The variational theorem, which is key to X-ray electron density energy calculation, holds only if the density matrices involved are N-representable. For extremely large molecular systems, it becomes beneficial to express the X-ray one-body density matrix in a kernel energy method (KEM) framework. In this work, we present the explicit form of the associated N-representable two-body density matrix and discuss its application in calculating molecular energy.