A Molecular Energy Decomposition Scheme for Atoms in Molecules.

An exact energy partition method based on a physically sound decomposition of the nondiagonal first-order and diagonal second-order density matrices put forward by Li and Parr (J. Chem. Phys. 1986, 84, 1704) is presented. The method splits the total energy into intra- and interatomic components and is applicable on quite general wave functions. To explore it numerically, the energy components of three test molecules (H2, N2, and LiH) have been computed using four different partitions of the charge density ρ(r) into atomic densities. Several aspects on the chemical bond and the relative importance of different components of the binding energy are analyzed. The merits of different partitions of ρ(r) are also discussed.