T: The space group generated from the generators is used. This may be useful if the calculation has to be performed for a lower symmetry than the actual symmetry of the solid. F: The space group of the solid is found by the program and used in the calculation. Furthermore, if some atoms are missing in category SITE they will be added to the basis. I.e. only one of the equivalent atoms must be supplied in SITE. After the basis has been completed it is recommended to use USESYM=F.