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Article Dans Une Revue Acta Crystallographica Section A : Foundations and Advances [2014-...] Année : 2012

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

Résumé

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

hal-01710507 , version 1 (16-02-2018)

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Agnieszka Poulain-Paul, Ayoub Nassour, Christian Jelsch, Benoit Guillot, Maciej Kubicki, et al.. A critical analysis of dipole-moment calculations as obtained from experimental and theoretical structure factors. Acta Crystallographica Section A : Foundations and Advances [2014-..], 2012, 68 (6), pp.715-728. ⟨10.1107/S0108767312034010⟩. ⟨hal-01710507⟩
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