A critical analysis of dipole-moment calculations as obtained from experimental and theoretical structure factors

摘要: Three models of charge-density distribution - Hansen-Coppens multipolar, virtual atom and kappa different complexities, numbers refined parameters, with variable levels restraints, were tested against theoretical high-resolution X-ray diffraction structure factors for 2-methyl-4-nitro-1-phenyl-1H-imidazole-5-carbonitrile. The influence the model, refinement strategy, multipole level treatment H atoms on dipole moment was investigated. turned out to be very sensitive strategy. Also, small changes in H-atom can greatly calculated magnitude orientation moment. best results obtained when kept positions determined by neutron anisotropic displacement parameters (obtained SHADE, this case) used. constraints values found superior free these parameters. It is also shown that over-parametrization multipolar although possibly leading better residuals, general gives worse moments.