count_beta_orbs_ij Function

    function count_beta_orbs_ij(csf_i, i, j) result(nOpen)
        ! function to count the number of 1s in a CSF det between spatial
        ! orbitals i and j
        type(CSF_Info_t), intent(in) :: csf_i
        integer, intent(in) :: i, j
        integer :: nOpen
        character(*), parameter :: this_routine = "count_beta_orbs_ij"

        integer :: k

        ASSERT(i > 0 .and. i <= nSpatOrbs)
        ASSERT(j > 0 .and. j <= nSpatOrbs)

        nOpen = 0

        ! quick and dirty fix to deal with the excitation range mask probs:
        ! do i always call that for the current det the excitation is
        ! calculated for?  i think so..
        do k = i, j
            if (csf_i%stepvector(k) == 1) then
                nOpen = nOpen + 1
            end if
        end do
    end function count_beta_orbs_ij