A theoretical study of linear beryllium chains: Full configuration interaction

We present a Full-CI study of Be_N (N = 2, 3, 4, 5) linear chains. A comparative study of the basis set effect on the reproduction of the energy profile has been reported. In particular, the 3s1p, 4s2p, 4s2p1d, 5s3p2d and 5s3p2d1f bases were selected. For the smallest chains (i.e. Be_2 and Be_3), smaller basis sets give dissociative energy profiles so large basis set are demanded for the reproduction of equilibrium minima in the structures. For Be_4 and Be_5 linear chains, the energy profiles show a minimum also by using the smallest basis sets, but largest ones gives a much stronger stabilization energy.For all the structures, two spin states have been studied: the singlet and the triplet. The energy separation of the two states, in the equilibrium region, is small and becomes smaller as the number of atoms in the chain increases.