ELECTRONIC CORRELATION AND THE SI(100) SURFACE: BUCKLING VERSUS NONBUCKLING.

THEORETICAL CLUSTER CALCULATIONS FOR THE SI(100) SURFACE INDICATE THAT THE USE OF DOUBLY OCCUPIED ORBITAL WAVEFUNCTIONS, SUCH AS THE CLOSED-SHELL HARTREE-FOCK (HF), LEAD TO AN ASYMMETRIC DIMER DESCRIPTION OF THE SURFACE. THE INCLUSION OF ELECTRON CORRELATION PRODUCES A SYMMETRIC DIMER DESCRIPTION WITH A GROUND STATE APPROXIMATELY 1. 0 EV BELOW THE MINIMUM OF THE HF BUCKLED DIMER. THERE ARE TWO LOW-LYING STATES OF THE SYMMETRIC DIMER (A SINGLET AND A TRIPLET) WITH VERY DIFFERENT GEOMETRIES. ENERGY MINIMIZATION CALCULATIONS INDICATE THAT A (2 * 1) STRUCTURE IS FAVORED OVER A C(2 * 2) STRUCTURE.IONIZATION POTENTIALS FOR SURFACE AND SI(2P) CORE ELECTRONSTHAT ARE CONSISTENT WITH CURRENT EXPERIMENTAL DATA ARE ALSOREPORTED.