add support for LDA/GGA+U

[bernstei]

Many systems of interest involve transition metals that are better described by LDA+U or GGA+U, so it would be nice to support those sorts of functionals (also hybrid functionals, but I gather those are already being planned, right?)

[phanish-suryanarayana]

Yes, LDA/GGA+U is another on our list of features to be incorporated. Hybrid functionals have already been implemented and tested. It should be released in the coming weeks.