Parametrization of a hybrid QM/MM potential to investigate the iodide−triiodide exchange reaction in iodide based ionic liquids

GALASSI, VANESA V.; KOHANOFF, JORGE J.; MARIO G DEL POPOLO

Limerick

Workshop; CECAM Workshop Nanoscale Simulators of Ireland Annual Meeting; 2018

University of Limerick

Iodide based room temperature ionic liquids (RTIL) have greatscientific and technological relevance as they are used aselectrolytes and charge-transfer solvents in dye-sensitized solarcells. Iodide based RTIL show a strikingly high electric conductivitydespite their high viscosity, a property that has been attributed toa Grotthuss-like transport mechanism involving the transfer of iodinemolecules between the ions making the I-/I3-redox couple [1,2].Our goal is toinvestigate the charge transfer pathway in the liquid phase of the aniodine-doped 1-buthyl-3-methylimidazolium iodide ([bmim][I]) sample.In this sense, hybrid QM/MM potentials yield an efficient alternativeto full ab initio calculations, which are prohibitive for simulatingreactive events in ionic liquids. We have parametrized thecross-terms of a QM/MM force field, where cations are treated withinthe framework of the molecular mechanics formalism (MM), while anionsand iodine molecules are treated quantum mechanically (QM).Parameters have been fitted to reproduce higher level theoreticalcalculations and experimental properties, such as the I2transfer pathway in a solid-state RTIL and the cohesive energy of thecrystalline phase of [bmim][I]. In the present work, we present anddiscuss the strengths and limitations of our QM/MM potential.[1] Verner KThorsmølle, Guido Rothenberger, Daniel Topgaard, Jan C Brauer,Dai-Bin Kuang, Shaik M Zakeeruddin, Björn Lindman, Michael Grätzel,and Jacques-E Moser. Extraordinarily efficient conduction in aredox-active ionic liquid. ChemPhysChem, 12(1):145?149, 2011.[2] Joás Grossi, Jorge J. Kohanoff, Niall J. English, Eduardo M. Bringa,and Mario G. Del Pópolo. On the mechanism of the iodide-triiodideexchange reaction in a solid-state ionic liquid. The Journal ofPhysical Chemistry B, 121(26): 6436?6441, 2017.