1. 1. 11 Physical Model Validation

All physical models have a range of validity where models are designed to obtain a simplified description of some physical mechanism under certain circumstances. If these assumptions are incorrect, the solution of the model might be wrong. Typical examples for physical assumptions are listed below.

• Low masses or energies for non-relativistic models
• Lattice temperature equals carrier temperature for isothermal models. Otherwise higher order models [11] must be used.

Several measures might be taken in order to avoid problems with physical models becoming invalid. In most cases the model is replaced by a refined and perhaps more elaborate or detailed model with extended range of validity. Sometimes it is possible to use refined models only in regions where extended parameter ranges are required.