OH radical in water from ab initio molecular dynamics simulation employing hybrid functionals

C Apostolidou, JOURNAL OF CHEMICAL PHYSICS, 151, 064111 (2019).

DOI: 10.1063/1.5107479

This work presents for the first time ab initio molecular dynamics simulations for the OH star-(H2O)(n) cluster with n = 0-5 and the OH radical in the bulk phase, using B3LYP as a functional. Furthermore, for OH star-w31, simulations with PBE0 and HSE03 are also investigated. In all systems, the OH radical is a stronger hydrogen bond donor than acceptor; a stronger hydrogen bond donor than water and a weaker hydrogen bond acceptor than water. Radial distribution functions (RDFs) reveal that for all systems, neither a hemibond between radical and water nor hydrogen abstraction is present. Comparisons with past simulations indicate that BLYP leads to artifacts, such as overstructuring of water in OH star-w31 and the hemibonded structure. In order to have strong hydrogen bonds with an extensive hydrogen bond network, at least four water molecules are necessary. RDFs as well as continuous dimer existence autocorrelation functions show that the OH radical is not disrupting the hydrogen bond network of water. In the bulk phase, the acceptor interaction is a very low probable interaction, whereas in the gas phase, it has a higher probability. The orientation of the water molecule around the OH radical is in the bulk liquid phase much less and in the gas phase enhanced, especially for the OH radical acting as a hydrogen bond donor toward one water molecule. PBE0 results for OH star-w31 in a strong hydrogen bond donor interaction compared to HSE03 and B3LYP, which has the weakest interaction. HSE03 leads to strong O-H interactions in OH star-w31, followed by PBE0 and B3LYP. Published under license by AIP Publishing.

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