Improved definition of bond orders for correlated wave functions

The definition of bond orders for singlet correlated wave functions is improved by adding a term providing the correct dissociation behaviour if the system dissociates into open-shell fragments.

45Highlights► Bond order indices: improving the definition for correlated singlet wave functions. ► The proposed correction provides correct dissociation behaviour if the system dissociates into open-shell fragments. ► Reconstruction of the ROHF spin density matrix from the total density matrix. ► Definition of a “pseudo spin density matrix” for correlated systems, to be used in the bond order formula.