create_heisenberg_fock_space_guga Function

    function create_heisenberg_fock_space_guga(n_orbs) result(heisenberg_fock)
        integer, intent(in) :: n_orbs
        integer(n_int), allocatable :: heisenberg_fock(:,:)

        integer :: i, n_up, n_down, j, s_tot
        integer(n_int), allocatable :: hilbert_space(:,:), temp_fock(:,:)

        allocate(temp_fock(0:0, 2**n_orbs), source = 0_n_int)

        j = 1
        do i = 0, n_orbs / 2

            n_up = n_orbs - i
            n_down = i

            s_tot = n_up - n_down

            hilbert_space = create_all_open_shell_dets(n_orbs, n_down, n_up)
            hilbert_space = csf_purify(hilbert_space, s_tot, n_orbs)

            temp_fock(:,j:j+size(hilbert_space,2)-1) = hilbert_space
            j = j + size(hilbert_space, 2)
        end do

        allocate(heisenberg_fock(0:0,j-1), source = temp_fock(:,1:j-1))

    end function create_heisenberg_fock_space_guga