  The systematic investigation of the ground state and fission properties of
even-even actinides and superheavy nuclei with $Z=90-120$ from the two-proton
up to two-neutron drip lines with proper assessment of systematic theoretical
uncertainties has been performed for the first time in the framework of
covariant density functional theory (CDFT). These results provide a necessary
theoretical input for the r-process modeling in heavy nuclei and, in
particular, for the study of fission recycling. Four state-of-the-art globally
tested covariant energy density functionals (CEDFs), namely, DD-PC1, DD-ME2,
NL3* and PC-PK1, representing the major classes of the CDFT models are employed
in the present study. Ground state deformations, binding energies, two neutron
separation energies, $\alpha$-decay $Q_{\alpha}$ values and half-lives and the
heights of fission barriers have been calculated for all these nuclei.
Theoretical uncertainties in these physical observables and their evolution as
a function of proton and neutron numbers have been quantified and their major
sources have been identified. Spherical shell closures at $Z=120$, $N=184$ and
$N=258$ and the structure of the single-particle (especially, high-$j$) states
in their vicinities as well as nuclear matter properties of employed CEDFs are
two major factors contributing into theoretical uncertainties. However,
different physical observables are affected in a different way by these two
factors. For example, theoretical uncertainties in calculated ground state
deformations are affected mostly by former factor, while theoretical
uncertainties in fission barriers depend on both of these factors.
