Hi,
Perhaps this is not directly related to the original post, but I think it could be a good thing to be more clear between CC2 and MP2 for ground state calculations (e.g. energies and geometries). I just followed a presentation where after optimizing the geometry with DFT, the "accurate" ground state energies were obtained using CC2. After asking why they prefer CC2 over MP2 for their energies, the answer was that it's a higher order method and therefore more accurate.
Christof's message is quite clear but I took a look at the RICC2 section of the manual but didn't find a warning that you should not use CC2 for ground state energies. Is it just that you spend more CPU time or do the results (ground state energies/geometries) get worse and, if so, by how much?
regards,
Olli