  We investigate the entrance channel dynamics for the reactions
$\mathrm{^{70}Zn}+\mathrm{^{208}Pb}$ and $\mathrm{^{48}Ca}+\mathrm{^{238}U}$
using the fully microscopic time-dependent Hartree-Fock (TDHF) theory coupled
with a density constraint. We calculate excitation energies and capture
cross-sections relevant for the study of superheavy formations. We discuss the
deformation dependence of the ion-ion potential for the
$\mathrm{^{48}Ca}+\mathrm{^{238}U}$ system and perform an alignment angle
averaging for the calculation of the capture cross-section. The results show
that this parameter-free approach can generate results in good agreement with
experiment and other theories.
