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Accurate charge density of trialanine : a comparison of the multipole formalism and the maximum entropy method (MEM)

Title data

Hofmann, Andreas ; Netzel, Jeanette ; van Smaalen, Sander:
Accurate charge density of trialanine : a comparison of the multipole formalism and the maximum entropy method (MEM).
In: Acta Crystallographica Section B. Vol. 63 (2007) Issue 2 . - pp. 285-295.
ISSN 2052-5206
DOI: https://doi.org/10.1107/S0108768106052153

Project information

Project financing: Deutsche Forschungsgemeinschaft

Abstract in another language

An accurate charge density study of trialanine is presented with the maximum entropy method (MEM), on the basis of the same reflection data as was used for a multipole refinement R{\"o}del {\it et al.} (2006). {\it Org. Biomol. Chem.} {\bf 4}, 475{--}481. With the MEM, the optimum fit to the data is found to correspond to a final value of {$\chi$}${\sp 2}$ which is less than its statistical expectation value {\it N}${\sb Ref}$, where {\it N}${\sb Ref}$ is the number of reflections. A refinement strategy is presented that determines the optimal goal for {$\chi$}${\sp 2}$. It is shown that the MEM and the multipole method are on a par with regard to the reproduction of atomic charges and volumes, general topological features and trends in the charge density in the bond critical points (BCPs). Regarding the values of the charge densities in the BCPs, agreement between quantum chemical calculations, the multipole method and MEM is good, but not perfect. In the case of the Laplacians, the coincidence is not as good and especially the Laplacians of the C{---}O bonds differ strongly. One of the reasons for the observed differences in the topological parameters in the BCPs is the fact that MEM densities still include the effects of thermal motion, whereas multipole densities are free from the effects of thermal motion. Hydrogen bonds are more convincingly reproduced by the MEM than by multipole models.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: maximum entropy method; multipole formalism; accurate charge density; peptides
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences > Chair Crystallography
Faculties
Faculties > Faculty of Mathematics, Physics und Computer Science
Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 26 Feb 2016 08:01
Last Modified: 26 Feb 2016 08:01
URI: https://eref.uni-bayreuth.de/id/eprint/31182