There are many macroscopic properties that can be calculated from
computer simulation of molecular systems e.g.
heat capacity, radial distribution functions or non-equilibrium properties such as diffusion coefficients.
However, here we will only
give a short perspective to the free energy calculations.
Reaction free energy (Helmholtz or Gibbs functions) is the
magnitude that describes the spontaneity of thermic processes in NVT and NPT
ensembles, respectively, that is, the tendency of molecular systems to associate and/or react.
In addition, under the framework of Transition State theory, it will describe the kinetics of such process.