Optimizing the geometry of stereoregular polymers. III. Polyyne and the basis set quasi-linear dependence

The ground-state geometry of polyyne is determined ab initio by crystal-orb ital calculations taking into account the long-range effects up to the thir d-order correction. The basis set quasi-linear dependence problem is addres sed in detail acid the impact of removing some dimensions of the atomic bas is set on the geometrical derivatives of the total energy is quantitatively evaluated. Comparisons with other theoretical works using either crystal-o rbital or molecular orbital procedures are carried out. (C) 2000 John Wiley & Sons, Inc.