Integration with the DIRAC software enables calculations using various relativistic Hamiltonians, such as the four-component Dirac and the X2C Hamiltonian, as well as a non-relativistic Hamiltonian. At the present stage, a CASCI/RASCI function using the MOs obtained from a Hartree-Fock (HF) calculation was employed as a reference function because CASSCF/RASSCF calculations would incur substantial computational expenses. The improved virtual orbital (IVO) method was used with the CASCI/RASCI approach to address the incomplete description of virtual orbitals obtained from HF calculations.