EXTRAPOLATION OF REAL-SPACE QUANTUM-CHEMICAL CALCULATIONS FROM FINITE-SIZE SUPER CELLS TO THE IDEAL INFINITE SYSTEM .2. APPLICATION TO ONE-DIMENSIONAL POLYMERS

Calculations of finite atomic clusters based on the Hartree-Fock self- consistent field theory are modified to model more closely the ideal b ehavior of the infinite system. The density matrix of the standard fin ite supercell calculation is extrapolated to an infinite supercell so that it contains information from a continuum of k points in the first Brillouin zone. This modification is incorporated into the self-consi stency loop of the MOPAC quantum chemistry program and leads to improv ed results compared to a standard finite supercell calculation. Heats of formation, bond lengths, and electronic properties converge more qu ickly to the correct ground-state values. For polyacetylene, we obtain a reduced bond-length alternation of Delta r = 0.084 Angstrom, which is in agreement with more sophisticated calculations containing electr on correlation effects. (C) 1994 John Wiley & Sons, Inc.