Midgley, Laura and Bourhis, Luc J. and Dolomanov, Oleg and Grabowsky, Simon and Kleemiss, Florian and Puschmann, Horst and Peyerimhoff, Norbert (2021) Vanishing of the atomic form factor derivatives in non-spherical structural refinement - a key approximation scrutinized in the case of Hirshfeld atom refinement. ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, A77. pp. 519-533. ISSN 2053-2733
Full text not available from this repository.Abstract
When calculating derivatives of structure factors, there is one particular term (the derivatives of the atomic form factors) that will always be zero in the case of tabulated spherical atomic form factors. What happens if the form factors are non-spherical? The assumption that this particular term is very close to zero is generally made in non-spherical refinements (for example, implementations of Hirshfeld atom refinement or transferable aspherical atom models), unless the form factors are refinable parameters (for example multipole modelling). To evaluate this general approximation for one specific method, a numerical differentiation was implemented within the NoSpherA2 framework to calculate the derivatives of the structure factors in a Hirshfeld atom refinement directly as accurately as possible, thus bypassing the approximation altogether. Comparing wR(2) factors and atomic parameters, along with their uncertainties from the approximate and numerically differentiating refinements, it turns out that the impact of this approximation on the final crystallographic model is indeed negligible.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | X-RAY-DIFFRACTION; ELECTRON-DENSITY; DATA-BANK; HYDROGEN-ATOMS; VALIDATION; NEUTRON; PROGRAM; ACID; quantum crystallography; refinement; non-spherical form factors |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Central Analytical Services |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 13 Sep 2022 05:00 |
| Last Modified: | 13 Sep 2022 05:00 |
| URI: | https://pred.uni-regensburg.de/id/eprint/47680 |
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