Journal Article10.1107/S0108767308005709
X-ray structure refinement using aspherical atomic density functions obtained from quantum-mechanical calculations.
Dylan Jayatilaka,Birger Dittrich +1 more
187
TL;DR: Contrary to current consensus in structure refinement, the anisotropic displacement parameters of H atoms can be reproduced from neutron diffraction measurements simply from a least-squares fit using the Hirshfeld atoms derived from the BLYP level of theory and including a simple point-charge model to treat the crystal environment.
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Abstract: An approach is outlined for X-ray structure refinement using atomic density fragments obtained by Hirshfeld partitioning of quantum-mechanical density fragments. Results are presented for crystal structure refinements of urea and benzene using these `Hirshfeld atoms'. Using this procedure, the quantum-mechanical non-spherical electron density is taken into account in the structural model based on the conformation found in the crystal. Contrary to current consensus in structure refinement, the anisotropic displacement parameters of H atoms can be reproduced from neutron diffraction measurements simply from a least-squares fit using the Hirshfeld atoms derived from the BLYP level of theory and including a simple point-charge model to treat the crystal environment.
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Citations
Hydrogen atoms can be located accurately and precisely by x-ray crystallography
TL;DR: It is shown that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A–H) that are in agreement with results from neutron diffraction mostly within a single standard deviation.
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Hirshfeld atom refinement
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TL;DR: A robust and fast system where modern chemical structure models replace the old assumptions, leading to correct structures from the model refinement against standard in-house diffraction data using no more than widely available software and desktop computing power is devised.
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