  The beryllium dimer and trimer are, despite their small number of electrons,
excellent systems for assessing electronic-structure computational methods.
With reference data provided by multi-reference averaged coupled-pair
functional calculations, we assess several variants of range-separated
density-functional theory, combining long-range second-order perturbation
theory or coupled-cluster theory with a short-range density functional. The
results show that i) long-range second-order perturbation theory is not
sufficient, ii) long-range coupled-cluster theory gives reasonably accurate
potential energy curves, but iii) provided a relatively large value of $\mu=1$
bohr$^{-1}$ for the range-separationparameter is used. The article is dedicated
to the memory of J\'anos G. \'Angy\'an.

Chemical Physics