Use fxc from Libxc for GGAs
The formula can be found here:
- http://journals.aps.org/prb/pdf/10.1103/PhysRevB.69.115106
- http://www.tddft.org/TDDFT2004/PracticalSessions/papers/ahlrichs_casida.pdf
This is related to MR !742.
Edited by Micael Oliveira