Electron‐pair density decomposition for core–valence separable systems

The electron pair density of a core‐valence separable system can be decomposed into three parts: core‐core, core‐valence, and valence‐valence. The core‐core part has a Hartree‐Fock like structure. The core‐valence part can be written as Γ_cv (1,2) = γ_c (1,1)γ_v (2,2) ? γ_c (1,2)γ_v (2,1) + γ_c (2,2)γ_v (1,1) ? γ_c (2,1)γ_v (1,2), where only the 1‐matrices from the core and valence orbitals contribute. The valence‐valence part is left to be determined from the reduced frozen‐core type wave function, which often contains the essential information on the electron correlation and the chemical bond. We demonstrate the analysis to the ground state of negative ion Li^? and 2¹Σ_u⁺ excited state of the Li₂ molecule. © 2012 Wiley Periodicals, Inc.