A theoretical study of linear beryllium chains: Full configuration interaction

We present a full configuration interaction 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 is 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 the largest ones give a much stronger stabilization energy. For all the structures, two spin states have been studied: the singlet and the triplet. It is shown that the energy separation of the two states, in the equilibrium region, is small and decays exponentially with respect to the number of atoms in the chain. Finally an interpolative technique allowing for the estimation of the long-chain parameters from shorter ones is presented.