- #26

DrDu

Science Advisor

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Just one point: The temperature does not enter the hamiltonian but is taken into account via a thermal ensemble where the occupation probability of an excited state of a molecule is given by Boltzmann factors exp (-E/kT), where E is the energy relative to the ground state.

Pressure effects, at least in gasses, are often calculated starting from a virial expansion, i.e. interactions of the molecules are considered according to the number of interacting molecules (2, 3, 4 etc.).