DENSITY-MATRIX REFINEMENT FOR MOLECULAR-CRYSTALS

The fitting of an idempotent density matrix to x-ray structure factors is discussed. If the density matrix is identified with a single, Slat er determinant of orbitals, then a model wave function can be recovere d, enabling the computation of two-electron properties as well as the usual one-electron properties derived from the electron density. Hence this approach is potentially superior to the usual multipole expansio n used in charge-density analysis, although the current are formalisms are only useful for molecular crystals of very small molecules. A pro cedure is described, and applications to one theoretical example (meth ylamine) and one experimental example (formamide) are presented.