TT-MULTIPLETS is a set of computer programs designed to calculate radiative transitions between two configurations, for example a dipolar transition simulating a 2p->3d x-ray absorption process. It is capable of simulating all core level spectroscopies.

The programs have all been written or modified by the late Theo Thole. They are maintained and distributed by Frank de Groot at Solid State Physics Laboratory (Univ. of Groningen, Netherlands). More information can be obtained from here