Q. Should I use geometry optimized by the SAC method for calculations of the vertical excitation energy with the SAC-CI method?

 

A. Using the optimized geometry with the SAC method is of course a good choice for the calculations of vertical excited states. However, the geometry optimization with the SAC method is costly and practically impossible for large molecules. You can use experimental or optimized geometry with less expensive method, if those geometries are enough accuracy. For further details, refer to our articles.