This keyword requests a general Complete Basis Set extrapolation of the MP2 energy [Nyden81, Petersson88, Petersson91, Petersson91a].
The method requires two parameters: the minimum number of pair natural orbitals and the integration grid, which are set with the CBSExtrapolate=NMin and Integral=Grid options, respectively.
The minimum number of pair natural orbitals defaults to 5 for the 6-31G**, 6-31G‡ and 6-311G** basis sets (with or without diffuse functions), and to 10 for the 6-311G basis set with (2df,p) or (3df,p) polarization functions (again, with or without diffuse functions). NMin must be specified in all other cases, or an error will result.
The default integration grid is the (99,590) grid; an alternate grid can be specified with the Integral=Grid keyword. The integration portion is a small part of the total CBS extrapolation computation, so this relatively large grid was chosen. See the description of the Integral keyword for a full discussion of the available grids.
Specifies N as the minimum number of pair natural orbitals.
Use localization based on populations in minimal basis [Montgomery00]. This is the default.
Use population localization as described in reference [Pipek89].
Use Boys localization [Boys60, Foster60, Boys66].
Do not use any localization.
Newton-Raphson population localization.
Newton-Raphson Boys localization.
Use 2nd order minimal population analysis.
Save the localized CBS orbitals to the read-write file. Note that they will replace the SCF orbitals.