trouble with M06-2X

Calculating the polarizability requires second derivatives of the exchange-correlation functional, and as stated in the documentation, second derivatives of the Minnesota functionals have not been implemented. The new (and still listed as experimental) NWXC module (https://nwchemgit.github.io/index.php/Release66:Density_Functional_Theory_for_Molecules#NWXC_...) potentially should be able to calculate those second derivatives through its automatic differentiation. Though as I stated, that module is still listed as experimental so check results with extra care (if it works at all).