Parsing hybrid functional parameters
Hybrid functionals have, by definition, a mixing parameter (typically abbreviated as alpha) that determines the fraction of Hartree-Fock/Exact Exchange mixed in. All libxc names come with defaults (most often alpha = 0.25), but many codes also allow the user to tweak these at will. Actually, it is quite common to recalibrate the alpha to a specific use case/observable. Hence, the parsers should be able to at least capture this value.
Similarly, the special subclass of short-range hybrid functionals introduce a screening parameter (abbreviated as omega) that cuts off the Exact Exchange after a certain range. This parameter too is common enough that it has to be captured.
- Parse and store the alpha parameter as a fraction (i.e. ]0,1[) in all electronic structure code that supports hybrid functionals, when present.
- Likewise, parse and store the omega parameter in Ångstrom.
- Default values do not have to be exposed (yet).
xc_hybrid_keywords contains the code-specific keywords (to be updated in the future).