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HF Dissociation in Water Clusters by Computer Simulations, with Alin Elena, Computational Scientist at Daresbury Laboratory

Image: Alin Elena, STFC
Alin Elena, STFC

Date: 28 January 2020   Time: 15:00 - 16:00

Alin Elena is a Computational Scientist at the Scientific & Technology Facilities Council's Daresbury Laboratory. Here his main activity relates to methods and software development, DL_POLY4. Alin has a strong interest in new technologies and High Performance Computing and their application to statistical physics. I am also involved in the Xeon Phi and many-core versions of DL_POLY. He studied for a Bachelor degree at University of Bucharest, Faculty of Physics and obtained a PhD at University College Dublin, School of Physics under the supervision of Prof Giovanni Ciccotti and Dr Simone Meloni. He currently works on implementing reactive force fields, forward flux sampling ?and Green-Kubo formalism to DL_POLY and has a passion for computational physics and number crunching.

Abstract: HF Dissociation in Water Clusters by Computer Simulations
We perform restrained hybrid Monte Carlo (MC) simulations to compute the equilibrium constant of the dissociation reaction of HF in HF(H2O)7. We find that the HF is a stronger acid in the cluster than in the bulk, and its acidity is higher at lower T. The latter phenomenon has a vibrational entropic origin, resulting from a counterintuitive balance of intra- and intermolecular terms. We find also a temperature dependence of the reactions mechanism. At low T (?225 K) the dissociation reaction follows a concerted path, with the H atoms belonging to the relevant hydrogen bond chain moving synchronously. At higher T (300 K), the first two hydrogen atoms move together, forming an intermediate metastable state having the structure of an eigen ion (H9O4+), and then the third hydrogen migrates completing the reaction. We also compute the dissociation rate constant, kRP. At very low T (?75 K) kRP depends strongly on the temperature, whereas it gets almost constant at higher T’s. With respect to the bulk, the HF dissociation in the HF(H2O)7 is about 1 order of magnitude faster. This is due to a lower free energy barrier for the dissociation in the cluster.

Location:  Laws Building Room 1.00, Queen Mary University of London, Mile End Campus
Website:  http://www.scd.stfc.ac.uk/Pages/Alin-Elena.aspx#