update_delta_psi Subroutine

    subroutine update_delta_psi()
        ! here, we add H^2 psi to delta_psi to generate the new delta_psi
        ! this might cause trouble as stochastic error is not averaged out,
        ! but we just carry over the error from the last iteration
        character(*), parameter :: this_routine = "update_delta_psi"

        ! add up delta_psi from the last iteration and spawnedParts (i.e. H^2 psi)
        call merge_ilut_lists(spawnedParts, dpsi_cache, spawn_ht, spawnBufSize, &
                              dpsi_size, maxSpawned)
        ! if semistochastic mode is run, we add the semistochastic spawns now
        ! because they have to be included in delta psi

        if (tSemiStochastic) call add_semistoch_spawns(spawnedParts, spawnBufSize, &
                                                       spawn_ht, maxSpawned, spawnBuf)

        ! cache delta_psi for the next iteration
        if (spawnBufSize > max_cache_size) call stop_all(this_routine, &
                                                         "Insufficient memory for creating delta_psi")

        dpsi_cache(:, 1:spawnBufSize) = spawnedParts(:, 1:spawnBufSize)
        dpsi_size = spawnBufSize

        ! for now, consider all entries in delta_psi as safe spawns for the next iteration
        if (tTruncInitiator) call set_initiator_flags_array(dpsi_cache, dpsi_size)
    end subroutine update_delta_psi