Therefore, calculations must include relativistic effects to simulate CPL spectra. A number of studies have been published that include such effects for molecules, which report circularly polarized phosphorescence (CPP, i.e., CPL from the lowest triplet state to the ground singlet state) for an organic molecule including vibrational effects at the Franck-Condon (FC) and Herzberg-Teller (FCHT) levels. These approaches need to be extended to periodic calculations.