When the junction is not operating at the nominal temperature as specified with the tnom parameter, a correction factor is applied to the critical current to account for the temperature difference. The superconducting energy gap and therefor the junction gap voltage will also change as a function of temperature.
In the TJM model, the energy gaps are always computed from the BCS integral equation involving superconducting transition temperature, Debye temperature, and operating temperature. The materials may be different on the two sides of the barrier. The junction gap voltage is the sum of the gap potentials of the two materials.
The critical current temperature variation again follows BCS theory. The temperature correction factor tcf multiplies the instance critical current to account for the temperature difference between operating and nominal temperatures.
tcf = (Vg/Vgnom)(tanh(eVg/4KT)/tanh(eVgnom/4KTnom))
Here, Vg is the computed gap voltage, e is the electron charge, K is Boltzmann's constant, T is temperature in Kelvin,