Ab initio treatment of electron correlations in polymers: Lithium hydride chain and beryllium hydride polymer

Correlated ab initio electronic structure calculations are reported for the polymers lithium hydride chain [LiH](infinity) and beryllium hydride [Be2H 4](infinity). First, employing a Wannier-function-based approach, the syste ms are studied at the Hartree-Fock level, by considering chains, simulating the infinite polymers. Subsequently, for the model system [LiH](infinity), the correlation effects are computed by considering virtual excitations fr om the occupied Hartree-Fock Wannier functions of the infinite chain into t he complementary space of localized unoccupied orbitals, employing a full-c onfiguration-interaction scheme. For [Be2H4](infinity), however, the electr on correlation contributions to its ground state energy are calculated by c onsidering finite clusters of increasing size modeling the system. Methods such as Moller-Plesset second-order perturbation theory and coupled-cluster singles, doubles and triples level of theory were employed. Equilibrium ge ometry, cohesive energy and polymerization energy are presented for both po lymers, and the rapid convergence of electron correlation effects, when bas ed upon a localized orbital scheme, is demonstrated. (C) 2000 American Inst itute of Physics. [S0021-9606(00)31110-2].