Possibility of using hybrid functionals

[exenGT]

Is it possible to use hybrid functionals like PBE0 and HSE in libxc?

Thanks, Jingyang

[antoine-levitt]

Ah, I thought we already had an issue for this. Not yet possible but the infrastructure is there so it shouldn't be hard to implement; it just needs somebody interested to actually do it.

[mfherbst]

Getting a basic version working should not be too hard, I agree.

However, to get it up to speed and get it to fully we still need a bit of extra infrastructure (communicating orbitals to the terms, efficient evaluation of the exact exchange, ways to not update the hybrid term at every SCF step). So some practical hacking at various parts of the code is required.

[antoine-levitt]

The terms already have the orbitals, and the code structure is OK I think. It's just missing a new term that computes the exchange, which should be very straightforward (and a great first contribution for someone interested : I'm tagging this as good first issue). It should work out of the box with direct minimization. Getting a scf solver to work needs more work, and to get it fast it needs the ACE method of Lin.