count_double_orbs Function

    function count_double_orbs(ilut) result(n_double_orbs)
        ! returns the number of doubly occupied orbitals for a given
        ! determinant.
        use DetBitOps, only: count_open_orbs
        integer(n_int), intent(in) :: ilut(0:niftot)
        integer :: n_double_orbs
        character(*), parameter :: this_routine = "count_double_occupancy"

        integer :: n_open_orbs

        n_open_orbs = count_open_orbs(ilut(0:nifd))

        ! the doubly occupied orbitals are just the number of electrons
        ! minus the number of open orbitals divided by 2
        n_double_orbs = (nel - n_open_orbs) / 2

    end function count_double_orbs