Issue 18, 2023

How do density functionals affect the Hirshfeld atom refinement?

Abstract

In this work, the effect of mixing different amounts of Hartree–Fock (HF) exchange with hybrid density functionals applied to the Hirshfeld atom refinement (HAR) of urea and oxalic acid dihydrate is explored. Together, the influence of using different basis sets, methods (including MP2 and HF) and cluster sizes (to model bulk effects) is studied. The results show that changing the amount of HF exchange, no matter the level of theory, has an impact almost exclusively on the H atom refinement parameters. Contrary to pure quantum mechanical calculations where good geometries are obtained with intermediate HF exchange mixtures, in the HAR the best match with neutron diffraction reference values is not necessarily found for these admixtures. While the non-hydrogen covalent bond lengths are insensitive to the combination of method or basis set employed, the X–H bond lengths always increase proportionally to the HF exchange for the analysed systems. This outcome is opposite to what is normally observed from geometry optimisations, i.e., shorter bonds are obtained with greater HF exchange. Additionally, the thermal ellipsoids tend to shrink with larger HF exchange, especially for the H atoms involved in strong hydrogen bonding. Thus, it may be the case that the development of density functionals or basis sets suitable for quantum crystallography should take a different path than those fitted for quantum chemistry calculations.

Graphical abstract: How do density functionals affect the Hirshfeld atom refinement?

Supplementary files

Article information

Article type
Paper
Submitted
03 sep 2022
Accepted
13 des 2022
First published
22 des 2022

Phys. Chem. Chem. Phys., 2023,25, 12702-12711

How do density functionals affect the Hirshfeld atom refinement?

B. Landeros-Rivera, D. Ramírez-Palma, F. Cortés-Guzmán, P. M. Dominiak and J. Contreras-García, Phys. Chem. Chem. Phys., 2023, 25, 12702 DOI: 10.1039/D2CP04098K

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