CC2 and ADC(2) are available in a very efficient implementation in Turbomole. All we had to do is produce some approximate non-adiabatic coupling terms. Our "trick" was the following (in a similar spirit to what they do for TDDFT): take only the single excitation part of the response vector, construct a renormalized CIS vector out of this, and compute the wavefunction overlap of these vectors at two different timesteps. The first numerical tests were very promising and it looks like this can really be a viable method.
The limitation is that CC and ADC (just as TDDFT) are not able to describe intersections with the closed shell ground state correctly. But, if you are interested in non-adiabatic excited state processes ADC(2) may be the method of choice for you. According to some of our previous experience, potential applications include:
- nπ* and ππ* crossings during excited state proton transfer
- energy and electron transfer
- excimer formation
- and in fact any application where you are not interested in the precise details of the activation to S0