M06

'''The M06 suite of functionals are a set of four meta-hybrid GGA DFT functionals. They are constructed with empirical fitting of their parameters, but constraining to the uniform electron gas.'''

'''The family includes the functionals M06-L, M06, M06-2X and M06-HF, with a different amount of exact exchange on each one. M06-L is fully local without HF exchange (thus it cannot be considered hybrid), M06 has 27% of HF exchange, M06-2X 54% and M06-HF 100%.'''

The advantages and utilities of each one are:


 * M06-L: Fast, Good for transition metals, inorganic and organometallics.
 * M06: For main group, organometallics, kinetics and non-covalent bonds.
 * M06-2X: Main group, kinetics.
 * M06-HF: Charge transfer TD-DFT, systems where self interaction is pathological.

'''The suite has a very good response under dispersion forces, improving one of the biggest deficiencies in DFT methods. The s6 scaling factor on Grimme's long range dispersion correction is 0.20, 0.25 and 0.06 for M06-L, M06 and M06-2X respectively. Compare it with the values of 1.05 for B3LYP or 0.70 for PBE0.'''