Long-range effects in optimizing the geometry of stereoregular polymers - IV: Explicit determination of the helical angle

摘要

We study the converging behavior of the analytical gradient of the energy per unit cell with respect to the helical angle in stereoregular polymers. Similarly to the other forces (with respect to nuclei coordinates or unit cell length), this gradient presents unique particularities. A technique based on multiple Taylor expansions is developed in order to evaluate accurately and directly the long-range contributions to this gradient. These LR contributions have analytical characteristics similar to the one of the stress-tensor, although the latter presents diverging sums. The method is tested on model system and is shown to be extremely efficient, allowing great improvement in accuracy at a negligible cost. (C) 2001 John Wiley & Sons, Inc. [References: 28]