A full explanation of the technique can be found in Chu, Shibing, et al. "Effects of Static Correlation between Spin Centers in Multicenter Transition Metal Complexes." Journal of chemical theory and computation 13.10 (2017): 4675-4683..
The technique has been developed by Shibing Chu, Daniele Bovi, Francesco Cappelluti, Alberto Giacomo Orellana, Herny Martin and Leonardo Guidoni.