Excess Models

Unless specifically amended, the excess Gibbs energy terms are modeled by the Redlich-Kister-Muggianu Model. Other excess models for the Gibbs energy are also implemented in Thermo‑Calc, such as e.g. Kohler and Toop-Kohler extrapolation models.

Thermo‑Calc is not restricted to binary interaction parameters. Ternary, quaternary and higher-order interaction parameters can also be used if there is enough information to evaluate these from experimental data. The ternary interaction parameters are identified by the degrees of the so-called ternary L parameter (i.e. 0, 1 and 2) in the command ENTER_PARAMETER. If the parameter is composition-independent, you only need a single interaction parameter with a degree of zero, i.e. only the ⁰L term. If there is a ternary composition-dependent interaction parameter, you must enter all three parameters (0,1 and 2). If such a ternary interaction parameter should be zero, then assign it a function which is zero. If the three interaction parameters have the same value, then that is identical to having a composition-independent ternary parameter.

ENTER_PARAMETER L(LIQUID,A,B,C;0) 298.15 +1000; 6000 N

ENTER_PARAMETER L(LIQUID,A,B,C;1) 298.15 +1000; 6000 N

ENTER_PARAMETER L(LIQUID,A,B,C;2) 298.15 +1000; 6000 N

is identical to

ENTER_PARAMETER L(LIQUID,A,B,C;0) 298.15 +1000; 6000 N

This also means that

ENTER_PARAMETER L(LIQUID,A,B,C;0) 298.15 +1000; 6000 N

ENTER_PARAMETER L(LIQUID,A,B,C;1) 298.15 +ZERO#; 6000 N

ENTER_PARAMETER L(LIQUID,A,B,C;2) 298.15 +ZERO#; 6000 N

is NOT identical to

ENTER_PARAMETER L(LIQUID,A,B,C;0) 298.15 +1000; 6000 N