Functionals

XC functionals are resolved through libxc at runtime. Any functional name libxc accepts works: short names ("LDA", "PBE", "B3LYP") and libxc XC_… identifiers both work.

Common choices

Name	Type	HF-exchange	Notes
LDA / SVWN	LDA	0 %	Slater + VWN5. Fast sanity check.
PBE	GGA	0 %	Workhorse for solid state.
BLYP	GGA	0 %	Classic molecular GGA.
PBE0	hybrid	25 %	PBE + Fock exchange.
B3LYP	hybrid	20 %	de-facto for organics.
HSE06	range-sep hybrid	25 % short-range	Needs range-separated Coulomb (coming later).

Accessing HF-exchange fraction

from vibeqc import Functional
fn = Functional("PBE0")
print(fn.hf_exchange_fraction())    # 0.25
print(fn.kind())                    # XCKind.GGA

Custom functional strings

libxc supports composition via ,:

fn = Functional("XC_LDA_X,XC_LDA_C_VWN")     # explicit Slater + VWN
fn = Functional("XC_GGA_X_PBE,XC_GGA_C_PBE")  # PBE made of separate components