Faster gradients for semiempirical methods

A new algorithm for the numerical evaluation of gradients in semiempirical methods is described. The method is approximately twice as fast as the sche mes currently employed and produces gradients of comparable accuracy. This method has been tested by comparing the results obtained by the new method with those of the previous numerical scheme, and also with those calculated analytically. The results of using the new gradients in geometry optimizat ions are also presented. (C) 1999 Kohn Wiley & Sons, Inc.