  The fusion dynamics on the formation of superheavy nuclei is investigated
thoroughly within the dinuclear system model. The Monte Carlo approach is
implemented into the nucleon transfer process for including all possible
orientations, at which the dinuclear system is assumed to be formed at the
touching configuration of dinuclear fragments. The production cross sections of
superheavy nuclei Cn, Fl, Lv, Ts and Og are calculated and compared with the
available data from Dubna. The evaporation residue excitation functions in the
channels of pure neutrons and charged particles are analyzed systematically.
The combinations with $^{44}$Sc, $^{48,50}$Ti, $^{49,51}$V, $^{52,54}$Cr,
$^{58,62}$Fe and $^{62,64}$Ni bombarding the actinide nuclides $^{238}$U,
$^{244}$Pu, $^{248}$Cm, $^{247,249}$Bk, $^{249,251}$Cf, $^{252}$Es and
$^{243}$Am are calculated for producing the superheavy elements with Z=119-122.
It is found that the production cross sections sensitively depend on the
neutron richness of reaction system. The structure of evaporation residue
excitation function is related to the neutron separation energy and fission
barrier of compound nucleus.
