Ha for the total and permanent QM/MM energies, and in order of 10 -5 for induced electrostatic QM/MM energies, respectively. When using a standard Coulombic interaction tensor (f (r cov ) = 0), the wave function optimization does not converge in some cases, especially when MM atoms are close to the QM subsystem. This indicates possible electron spill-out and consequent failure in wavefunction optimization.