Broken-symmetry natural orbital (BSNO)-Mk-MRCC study on the exchange coupling in the binuclear copper(II) compounds

► The magnetic interactions of binuclear copper(II) species are evaluated by Mk-MRCCSD method. ► Broken-symmetry natural orbitals are examined for the Mk-MRCCSD computations. ► The Mk-MRCCSD method can be applicable to the magnetic behaviors in binuclear copper(II) systems.