build_initial_delta_psi Subroutine

    subroutine build_initial_delta_psi()
        character(*), parameter :: this_routine = "build_initial_delta_psi"
        ! build delta_psi as  psi(delta_t) - psi(0), where psi(delta_t) is the current population
        ! and psi(0) the backup stored in popsfile_dets
        if (allocated(popsfile_dets)) then
            call add_ilut_lists(int(TotWalkers), backup_size, .true., CurrentDets, popsfile_dets, &
                                dpsi_cache, dpsi_size, -1.0_dp)

            ! we do not need popsfile dets anymore
            deallocate(popsfile_dets)
        else
            call stop_all(this_routine, "Backup buffer not allocated")
        end if
    end subroutine build_initial_delta_psi