Analytic second derivatives inside ADF

The functionality of the analytic second derivatives program SD has been moved inside the ADF program. In ADF one needs to use the AnalyticalFreq block keyword. Besides the LDA potential, one can now also use the GGAs BP86, PBE, RPBE, revPBE, BLYP, OLYP, and OPBE. A bug has been fixed for unrestricted calculations. Because this method is much faster and also seems more robust than numerical frequency calculations, the analytic second derivatives are now the new default in the ADF-GUI.

The Hessian can also be calculated for only some atoms, in which case a semi-empirical estimate is used for the rest. This can lead to big time savings when an approximate Hessian is needed for a transition state search of a big molecule.