sort_orbitals Subroutine

    subroutine sort_orbitals(nI, par_opt)
        !Sort oribtals and gives the parity of the unsorted list with respect to the sorted one.
        !Use this instead of the default sort when parity is needed.
        !The default sort has issues in calculating parity.

        integer, intent(inout) :: nI(:)
        integer, intent(out), optional :: par_opt
        integer :: temp, par
        integer :: i, j, num
        logical :: swapped

        num = size(nI)
        !Bubble sort
        par = 1
        do j = num - 1, 1, -1
            swapped = .FALSE.
            do i = 1, j
                if (nI(i) > nI(i + 1)) then
                    temp = nI(i)
                    nI(i) = nI(i + 1)
                    nI(i + 1) = temp
                    swapped = .TRUE.
                    par = -1 * par
                end if
            end do
            if (.not. swapped) exit
        end do

        if (present(par_opt)) par_opt = par

    end subroutine sort_orbitals