Natural molecular shells as open subsystems of small molecules

We compare the first few natural molecular shells of several small molecules to the corresponding “restricted Hartree‐Fock,” “second‐order Møller‐Plesset,” and “local density approximation” molecular shells. Occupation probabilities of each molecular shell are computed ab initio, especially the single‐occupation and double‐occupation probabilities, that is, the probabilities that the molecular shell is occupied by exactly one electron or by exactly two electrons. We observe that among corresponding molecular shells, the natural molecular shell has the least single‐occupation probability and the greatest double‐occupation probability. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011