Perspectives for hybrid ab initio/molecular mechanical simulations of solutions: from complex chemistry to proton-transfer reactions and interfaces

As a consequence of the ongoing development of enhanced computational resources, theoretical chemistry has become an increasingly valuable field for the investigation of a variety of chemical systems. Simulations employing a hybrid quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) technique have been shown to be a particularly promising approach, whenever ultrafast (i.e., picosecond) dynamical properties are to be studied, which are in many cases difficult to access via experimental techniques. Details of the quantum mechanical charge field (QMCF) ansatz, an advanced QM/MM protocol, are discussed and simulation results for various systems ranging from simple ionic hydrates to solvated organic molecules and coordination complexes in solution are presented. A particularly challenging application is the description of proton-transfer reactions in chemical simulations, which is a prerequisite to study acidified and basic systems. The methodical requirements for a combination of the QMCF methodology with a dissociative potential model for the description of the solvent are discussed. Furthermore, the possible extension of QM/MM approaches to solid/liquid interfaces is outlined.