Capabilities of chemical simulation methods in the elucidation of structure and dynamics of solutions

As a result of recent methodological developments in connection with enhanced computational capacity, theoretical methods have become increasingly valuable and reliable tools for the investigation of solutions. Simulation techniques utilizing a quantum mechanical (QM) approach for the treatment of the chemically most relevant region so-called hybrid quantum mechanical/molecular mechanical (QM/MM) simulations have reached a level of accuracy that often equals or may even surpass experimental methods. The latter is true in particular whenever ultrafast (i.e., picosecond) dynamics prevail, such as in labile hydrates or structure-breaking systems. The recent development of an improved QM/MM framework, the quantum mechanical charge field (QMCF) ansatz, enables a broad spectrum of solute systems to be elucidated. As this novel methodology does not require any solute solvent potential functions, the applicability of the QMCF method is straightforward and universal. This advantage is bought, however, at the price of a substantial increase of the QM subregion, and an attendant increase in computational periods to levels of months, and even a year, despite parallelizing high-performance computing (HPC) clusters. Molecular dynamics (MD) simulations of chemical systems showing increasing complexity have been performed, and demonstrate the superiority of the QMCF ansatz over conventional QM/MM schemes. The systems studied include Pd2+, Pt2+, and Hg22+, as well as composite anions such as PO43- and ClO4-.