Thermodn. properties can be calcd. from some selected function; such as the thermal equation of state, the fundamental equation or Helmholtz energy function, or the Gibbs energy function. These functions can be detd. using statistical thermodn., the science that relates thermodn. functions to intermol. potentials. Quantum mechanics must then be invoked to investigate the reasons for the interaction forces between mols. Computer simulations (mol. dynamics and Monte Carlo) can then be performed once accurate pair potentials have been established.