CBS-4M
CBS-QB3
CBS-APNO?
They are various Complete Basis Set (CBS) methods of Petersson and coworkers for computing very accurate energies
Q2: how many calculations they include?
It includes geometry optimization and frequency calculations.
It include MP2, MP4, CCSD calculations too.
Q3: why no basis sets are required in the Gaussian input file?
These methods will automatically assign basis sets for atoms.
