Chemical reactions, quantum dynamics basic properties

Mary Jo Nye enumerates the topics treated in the Journal as molecular spectroscopy and molecular structures, the quantum mechanical treatment of electronic structure of molecules and crystals and the problem of chemical binding, the kinetics of chemical reactions from the standpoint of basic physical principles, the thermodynamic properties of substances and calculation by statistical mechanical methods, the structure of crystals, and surface phenomena. M.J. Nye, From Chemical Philosophy to Theoretical Chemistry. Dynamics of Matter and Dynamics of Disciplines (Berkeley University of California Press 1993), 254. Many of these were considered by Barriol, as we will see later in this chapter. 

The most basic approach to carry out MD simulations for larger systems is to use classical force fields. A variety of different force fields for molecular mechanics (MM) simulations has been developed,which are mainly intended to describe the non-reactive dynamics of large systems. In particular in the field of biochemistry force fields play an essential role to study the complex properties of large biomolecules. However, classical force fields require the specification of the connectivity of the atoms. Therefore, they are not able to describe chemical reactions, i.e., the making and breaking of bonds. To describe reactions, they can be combined with quantum mechanical (QM) methods in so-called QM/MM simulations. In recent years also reactive force fields , e.g. ReaxFF, have been introduced, which overcome this limitation. However, these reactive force fields are typically highly adapted to specific systems by analytic terms customized to describe e.g. certain bonding situations, and only a few applications have been reported so far. 

---