Enthalpy, heat capacity and density

5 Physicochemical properties of liquids from MD or MC simulations 9.5.1 Enthalpy, heat capacity and density 

The calculated density of the computational system is evaluated by simply dividing the mass within the computational box by its volume after equilibration at a certain temperature and pressure. The enthalpy of vaporization is a measure of the intermolecular cohesion in the liquid, and the largest contribution to this quantity naturally comes from the intermolecular potential energy. The complete expression is  

The variation in potential energy, AE, is estimated by the difference in average energies over NVT simulations at different temperatures. 3R accounts for the kinetic equipartition contribution (see Section 7.2), and Cv(vibr) corrects for the vibrational constraints imposed in the simulation (for example by the SHAKE algorithm), and can be estimated by the usual quantum statistical mechanics formulas (equation 7.30) if the vibrational frequencies are known. 

The thermal expansion coefficient and the isothermal compressibility can be estimated as [9,12]  

United-atom simulations except AA, all-atom simulations. 

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