Checks that POTCARs are valid within a pre-defined input set. This ensures that calculations performed using different InputSets are not compared against each other. Entry.parameters must contain a "potcar_symbols" key that is a list of all POTCARs used in the run. Again, using the example of an Fe2O3 run using Materials Project parameters, this would look like entry.parameters["potcar_symbols"] = ['PAW_PBE Fe_pv 06Sep2000', 'PAW_PBE O 08Apr2002'].