State of the Relevant Quantum Chemical Art
For ground states it is meaningless to try to evaluate accuracy of methods without a systematic study of basis set convergence. For ground states the basis set problem is solved for 1st and 2nd and main group 3rd row
Methods for electronically excited states all scale poorly
- multireference CI (prohibitively expensive for large systems)
- multireference perturbation theory (convergence is still open question)
- coupled cluster methods (promising but still demanding)
- basis sets still are a problem for non-valence excited states
- spin orbit coupling will be important, and nonadiabatic coupling also
Electron affinity calculations by CI share many of the difficulties of electron scattering (balancing N & N+1 electron correlation) which are largely solved by other modern methods for bound anions