diagonalize_core Subroutine

    subroutine diagonalize_core(e_value, e_vector, rep)
        real(dp), intent(out)  :: e_value
        HElement_t(dp), intent(out), allocatable :: e_vector(:)
        type(core_space_t), intent(in) :: rep
        type(DavidsonCalcType) :: davidsonCalc
        integer :: ierr
        character(*), parameter :: t_r = "diagonalize_core"

        call create_sparse_ham_from_core(rep)

        ! Call the Davidson routine to find the ground state of the core space.
        call perform_davidson(davidsonCalc, parallel_sparse_hamil_type, .true.)

        e_value = davidsonCalc%davidson_eigenvalue
        allocate(e_vector(rep%determ_space_size))
        e_vector = davidsonCalc%davidson_eigenvector

        write(stdout, '(a30)') "Davidson calculation complete."
        write(stdout, '("Deterministic total energy:",1X,f15.10)') &
            e_value + Hii

        call neci_flush(stdout)

        call DestroyDavidsonCalc(davidsonCalc)
        ! call LogMemDealloc(t_r, DavidsonTag, ierr)
        deallocate(hamil_diag, stat=ierr)
        call LogMemDealloc(t_r, HDiagTag, ierr)
        call deallocate_sparse_ham(sparse_ham, SparseHamilTags)

    end subroutine diagonalize_core