The MP2-F12, CCSD-F12, and UCCSD-F12 methods must use conventional (non-density fitted) spin-restricted Hartree-Fock reference functions (HF or RHF).
DF-HF cannot be used for these methods. This restriction is necessary to ensure that the Fock matrix is diagonal and
consistent with the integrals used in these methods.
For DF-MP2-F12, DF-LMP2-F12, and DF-RMP2-F12 either HF or DF-HF reference functions can be used.
Currently, only finite dipole fields can be applied, other perturbations are not yet supported.
ECPs can be used, but this is still experimental and not extensively benchmarked.
The Douglas-Kroll-Hess or eXact-2-Component Hamiltonians cannot currently be used in combination with F12 methods.