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Novel SCS-IL-MP2 and SOS-IL-MP2 Methods for Accurate Energetics of Large-Scale Ionic Liquid Clusters

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journal contribution
posted on 11.08.2015, 00:00 authored by Jason Rigby, Santiago Barrera Acevedo, Ekaterina I. Izgorodina
Accurate energetics of intermolecular interactions in condensed systems are challenging to predict using highly correlated quantum chemical methods due to their great computational expense. Semi-Coulomb systems such as ionic liquids, in which electrostatic, dispersion, and induction forces are equally important, represent a further challenge for wave function-based methods. Here, the application of our recently developed SCS-IL-MP2 and SOS-IL-MP2 methods is reported for ionic liquid clusters of two and four ion pairs. Correlation interaction energies were found to be within 1.5 kJ mol–1, on average, per ion pair of the CCSD­(T)/CBS benchmark, thus introducing a marked improvement by a factor of 4 to conventional MP2 within the complete basis set. The fragment molecular orbital (FMO) approach in combination with both SCS-IL-MP2 and SOS-IL-MP2 has been shown to provide a reliable and computationally inexpensive alternative to CCSD­(T)/CBS for large-scale calculations of ionic liquids, thus paving the way toward feasible ab initio molecular dynamics and development of reliable force fields for these condensed systems.