Improved meta-GGA Correlation Functional of the Lap Family.

A new correlation functional of the Lap series is derived based on a more elaborated form of correlation wave vectors. Its validation is carried out within two different codes:  deMon-KS3 and Q-Chem 3.0. In deMon the implementation in a post-SCF manner is similar to the preceding BLap3 and Bmτ1 schemes. In Q-Chem the new functional is programmed self-consistently using the integration by parts procedure for the matrix elements. The post-SCF version of the functional deals with three fitting parameters; the previous Lap3 and τ1 functionals have four and five parameters, respectively. The SCF implementation requires only two fitting parameters. Preliminary comparative tests are discussed.