SCALEE = [real]
Default: SCALEE = 1
Description: This tag specifies the scaling constant (coupling parameter) of the energies and forces.
In thermodynamic integration the free energy difference between two systems is defined as
Here and describe the potential energies of a fully-interacting and a non-interacting reference system, respectively. The interaction of the constituents within the system is controlled via the coupling parameter . The SCALEE sets the value for the coupling constant.
Two possible options are available for the reference system:
- Ideal gas:
Usually the thermodynamic integration is carried out from the ideal gas to the liquid state.
- Harmonic solid
If the file DYNMATFULL exists in the calculation directory (from a previous calculation using PHON_NSTRUCT=-1) and SCALEE1, the second order Hessian matrix is added to the force and thermodynamic integration from a harmonic model to a fully interacting system is carried out. Here the Hamiltonian for a certain integration point along the thermodynamic integration pathway is given as