# ESPF QM/MM single-point energy.
#
# System: a water dimer (water_dimer.pdb).  QM region = the FIRST water
# (PDB atoms 0,1,2); the SECOND water is MM (TIP3P point charges).  The MM
# charges polarize the QM density through the ESPF operator.  Requires the
# optional OpenMM backend (pip install openmm).
[input]
system     = water_dimer.pdb 0 1 2   # PDB path + 0-based indices of the QM atoms
charge     = 0
runtype    = energy                  # single-point energy (+ requested properties)
method     = hf                      # HF/DFT driver (functional below picks DFT)
functional = bhhlyp                  # half-and-half hybrid; empty => plain HF
basis      = 6-31g*
qmmm_flag  = True                    # turn on QM/MM; without it [qmmm] is ignored

[scf]
type         = rhf                   # closed-shell reference for the QM region
multiplicity = 1

[qmmm]
forcefield_files = tip3p.xml         # OpenMM force field for the MM water
cutoff           = NoCutoff          # isolated (non-periodic) cluster
embedding        = electrostatic     # full ESPF electrostatic embedding