Octupole deformation in the ground states of even-even nuclei: A global analysis within the covariant density functional theory

A systematic investigation of octupole-deformed nuclei is presented for even-even systems with $Z\ensuremath{\le}106$ located between the two-proton and two-neutron driplines. For this study we use five most-up-to-date covariant energy density functionals of different types, with a nonlinear meson coupling, with density-dependent meson couplings, and with density-dependent zero-range interactions. Pairing correlations are treated within relativistic Hartree-Bogoliubov theory based on an effective separable particle-particle interaction of finite range. This allows us to assess theoretical uncertainties within the present covariant models for the prediction of physical observables relevant for octupole-deformed nuclei. In addition, a detailed comparison with the predictions of nonrelativistic models is performed. A new region of octupole deformation, centered around $Z\ensuremath{\sim}98,N\ensuremath{\sim}196$ is predicted for the first time. In terms of its size in the $(Z,N)$ plane and the impact of octupole deformation on binding energies this region is similar to the best known region of octupole-deformed nuclei centered at $Z\ensuremath{\sim}90,N\ensuremath{\sim}136$. For the later island of octupole-deformed nuclei, the calculations suggest substantial increase of its size as compared with available experimental data.