CTCTCT: Computational techniques and chemical theory of charge transfer (featuring dispersion)

Abstract

Intermolecular interactions are essential to model ionic liquid (IL) and deep eutectic propellent (DeEP) properties accurately. Charge transfer (CT) is important especially in protic ILs and DeEPs, which involve complex intermolecular interactions. Despite this, CT has not been well investigated and often not well defined due to strong electrostatic interactions which often overshadow the contributions of CT. Dispersion interactions also play an important role because they exhibit stabilizing effects in bulky ILs and DeEPs. Therefore, modeling such systems requires a fundamental understanding of intermolecular interactions and the development of ab initio methods that can accurately compute interaction energies. This dissertation elaborates theoretical approaches that can be used to model the interactions found in ILs, DeEPs and other chemical systems: 1) The benchmark results of a novel method to correct dispersion using the effective fragment potential (EFP) method are explained. 2) the efficacy of using fragmentation methods, as well as the application of the EFP method to model ILs is assessed. 3) Intermolecular interactions and hydrogen bond (H-bond) interactions in IL and DeEP clusters based on EFP and quasiatomic orbital (QUAO) analysis are discussed. 4) The CT analytic energy gradient in the effective fragment molecular orbital (EFMO) method is derived. The implementation of the analytic CT energy gradient is also proposed, which can facilitate more accurate modeling of bulk ionic systems in future works.