Setting Reference States

If you want to specify a non-default reference state for one or several of your system components, then you do this with the SET_REFERENCE_STATE command. In the following example, the reference states for Au and Cu are set to the liquid phase at current temperature (*) and a pressure of 1E5 Pa.

SET_REFERENCE_STATE AU LIQ * 1E5
SET_REFERENCE_STATE CU LIQ * 1E5

In order for these reference states to be taken into account, the R suffix must be used when the measurement of the enthalpy per mole of the system is entered for an experiment.

You can use the reference state suffix R for some thermodynamic variables to calculate their value with respect to a reference state that you have previously set for a system component with the SET_REFERENCE_STATE command in POLY (or in response-driven modules such as the POURBAIX module). The value of energy-related variables that are used with the R suffix depends on the reference states of all the components in the defined system.

It is possible to use an R suffix on all compositional extensive state variables as well, but the value of the state variable is always the same, with or without the suffix.

If the reference state for a system component is the default reference state (the stable reference state (SER) which is defined in a Thermo‑Calc database), then MUR(comp)= MU(comp), ACR(comp)= AC(comp) and LNACR(comp)= LNAC(comp).

In the case of some thermodynamic variables, you can also use the R suffix to express chemical potentials and activities of species relative to some single-substitutional-lattice solution phases (such as aqueous solution, gaseous mixture, metallic liquid solution, slag mixture or MO solid solution). These state variables are MU(sp,ph),  MUR(sp,ph),  AC(sp,ph),  ACR(sp,ph), LNAC(sp,ph) and LNACR(sp,ph).

The reference states and standard states of various solution species are pre-defined for some solution phases in some databases. For all solution species in any solution model in any database, it is always the case that MUR(sp,ph)= MU(sp,ph), ACR(sp,ph)= AC(sp,ph) and LNACR(sp,ph)= LNAC(sp,ph).