A calculation of this magnitude would be too demanding regarding both CPU time and memory requirements. To reduce the number of singly excited determinants we employed a commonly used truncation of the wavefunction. The squared expansion coefficients were first sorted in descending order. Then, the configurations were taken from the ordered list to the overlap calculation until the sum of the squared expansion coefficient reached a threshold of 0.996 for Chl D1 Pheo D1 pair and 0.994 for P D1 P D2 pair. In this way, the number of determinants was reduced to only several thousands which led to a significant reduction of computational costs while maintaining accuracy.