LOW-LYING STATES OF ALC2 AND SIC2+ - COMPETITION BETWEEN LINEAR AND CYCLIC CONFIGURATIONS

An ab initio study has been carried out for the isoelectronic systems SiC2+ and AlC2. In both cases a linear state is found to lie the lowest in energy at the Hartree-Fock level. However, correlation effects tend to favour cyclic structures. Although for SiC2+ Møller-Plesset and configuration interaction calculations provide different energy orders, the cyclic state is likely to be the ground state. In the case of AlC2 all correlated calculations show a cyclic structure to be the ground state. The electronic structure of the low-lying states of both systems is discussed, with special attention to the differences between Al and Si compounds. © 1990.