# Spin-flip TDDFT / 6-31G* / BHHLYP on H2O
# A high-spin (triplet) ROHF reference is spin-flipped down to reach the
# singlet manifold. This deck computes the SF-TDDFT energies and the gradient
# of the lowest SF root (the multiconfigurational ground state, grad=3 here).
[input]
system=
   8   0.000000000   0.000000000  -0.041061554
   1  -0.533194329   0.533194329  -0.614469223
   1   0.533194329  -0.533194329  -0.614469223
charge=0
runtype=grad            # energy + gradient; use runtype=energy for energy only
basis=6-31g*
functional=bhhlyp       # half-and-half functional recommended for spin-flip
method=tdhf             # the [tdhf] response engine drives SF-TDDFT

[guess]
type=huckel             # extended-Huckel initial orbitals

[scf]
multiplicity=3          # HIGH-SPIN triplet reference (the SF starting point)
type=rohf               # SF-TDDFT requires an ROHF reference

[tdhf]
type=sf                 # spin-flip TDDFT (not rpa/tda/mrsf)
nstate=3                # number of spin-flip roots to solve

[properties]
grad=3                  # gradient of SF root 3 (for SF, root 1 is the lowest/S0)