  The framework of nuclear energy density functionals is applied to a study of
the formation and evolution of cluster states in nuclei. The relativistic
functional DD-ME2 is used in triaxial and reflection-asymmetric relativistic
Hartree-Bogoliubov calculations of relatively light $N = Z$ and neutron-rich
nuclei. The role of deformation and degeneracy of single-nucleon states in the
formation of clusters is analysed, and interesting cluster structures are
predicted in excited configurations of Be, C, O, Ne, Mg, Si, S, Ar and Ca $N =
Z$ nuclei. Cluster phenomena in neutron-rich nuclei are discussed, and it is
shown that in neutron-rich Be and C nuclei cluster states occur as a result of
molecular bonding of $\alpha$-particles by the excess neutrons, and also that
proton covalent bonding can occur in $^{10}$C.

Nuclear Theory