I need to compute extremely accurate single point energies using the coupled cluster method. The methods to be employed scale largely with the number of basis functions. A few basis functions may have a huge impact in the computational cost.
I planned assigning a 3ζ basis set to a central atom, and 2ζ for the surrounding atoms. I cannot compute everything at 3ζ.
Clearly, these small basis sets are intended for estimate the contribution of high excitation.
Are there any reason which prevent this mixture, or any argument supporting the usage of 2ζ for every atom?