Molecular Associations Determined from Free Energy Calculations

Abstract

In this chapter we describe the development and implementation of a computational method able to produce free energies in multiple dimensions, descriptively named the free energies from adaptive reaction coordinate forces method (FEARCF). We use this method to investigate the structure of associative liquids such as water. Important chemical phenomena such as the free energy of ion pairing in methanol have been studied using the FEARCF method as have the reaction surfaces of chemical reactions in solution. More recently, a multidimensional intermolecular orientational free energy was developed from FEARCF. This multidimensional intermolecular free energy W(r, θ1, θ2, ϕ) provides means to measure the orientationally dependent molecular interactions, that are necessary for applications in complex systems such as proteins, where molecular anisotropic features govern the structure. It is a highly informative free energy volume and is shown to probe the thermodynamic nature of water’s tetrahedral local structure.