Modelling chemical reactions in (explicit) solvents

Author: Guest blogger

Posted: 18 Nov 2019 | 16:02

Arthur’s Seat in Edinburgh. St Andrews should be straight ahead.

Nicolas Sieffert was an HPC-Europa3 visitor to the University of St Andrews in summer 2018 and again in 2019. In this blog post he describes his two trips to Scotland.

Hi there! I am Nicolas Sieffert, associate professor in computational chemistry at the University Grenoble Alpes (France). I visited the UK for nine weeks under the HPC-Europa3 transnational access programme and was hosted by Prof. M. Bühl at the University of St Andrews (UK), with HPC resources and technical assistance provided by EPCC.

My research is devoted to the understanding of how the dynamics and the solvent environment influence the structure, the stability and the reactivity of metal complexes, in the fields of catalysis or liquid-liquid extraction. For that purpose, I study the dynamics of metal complexes in different solvent environments, using Density Functional Theory Molecular Dynamics simulations (DFT-MD). Free energies of reaction and of activation of elementary reaction steps are computed using advanced sampling techniques, such as metadynamics.

In the framework of the HPC-Europa3 programme, I worked in collaboration with Prof. M. Bühl to investigate the speciation of uranyl in liquid ammonia. In the first part of the project, we developed a cost-effective protocol allowing for the computation of free energies for coordination (and decoordination) of NH3 to UO22+ in ammonia solution. The latter is based on “static” Density Functional Theory calculations, in conjunction with a Polarisable Continuum Model (PCM) to account for solvation effects. This protocol has been carefully validated both against CCSD(T) calculations (for the intrinsic binding energies) and against DFT-MD simulations including explicitly-represented ammonia molecules, at finite temperature (for the solvation effects).

This work has been published in the themed collection of Chemical Communications “New molecules and materials from the f-block” (see: Sieffert, N.; Thakkar, A.; Bühl, M. Modelling uranyl chemistry in liquid ammonia from density functional theory. Chem. Commun. 2018, 54, 10431, link) and was presented at the Transnational Access Meeting 2018, held in Edinburgh on the 23rd October.

Further work on this topic is ongoing, and is devoted to study complexation properties of uranyl in liquid ammonia, using DFT-MD/metadynamics simulations.

Paragliding near Loch Leven.

Besides working, I really enjoyed my stay in Scotland. The city of St Andrews has a particular charm, making everyday life there particularly pleasant. In my free time, I took the opportunity to explore Scotland by different means: walking in the streets of Edinburgh, riding bikes on coastal paths through the country, or paragliding over the stunning Scottish hills.