merge_spawn Subroutine

    subroutine merge_spawn(nspawn, prefactor)
        use real_time_data, only: nspawnMax
        implicit none
        integer :: nspawn
        real(dp) :: prefactor
        ! truncate the number of spawns from a single determinant
        ! for now, use as a threshold a multiple of the average population
        ! for a full SpawnVec
        if (nspawn > nspawnMax) then
            prefactor = nspawn / real(nspawnMax, dp)
            nspawn = nspawnMax
        else
            prefactor = 1.0_dp
        end if
        ! the prefactor is used to unbias therefor
    end subroutine merge_spawn