Accurate pseudopotential local-density-approximation computations for neutral and ionized dimers of the IB and IIB groups

We have implemented an efficient algorithm to compute properties of linear molecules in the pseudopotential local-density-approximation (LDA) framework. Orbitals are expanded in an orthogonal and complete basis set of cylindrical waves. A large number of basis functions is dealt with using an iterative procedure requiring a number of operations proportional to the size of the basis set to the power 3/2. This favorable scaling law makes it possible to approach the LDA limit for molecules with s, p, and d valence electrons. We present results for homonuclear dimers of the IB and IIB elements. Comparison with previous computations for the IB dimers points out the advantages of our extended and unbiased basis set. We show that the LDA is able to account for many of the qualitative features characterizing the bonding of the IIB dimers, although important quantitative discrepancies remain in the comparison with experiment. Finally, we investigate the role of the closed-shell d electrons in the bonding of all these molecules.