Geometry optimization with QM/MM, ONIOM, and other combined methods. I. Microiterations and constraints.
Vreven T, Morokuma K, Farkas O, Schlegel HB, Frisch MJ. Geometry optimization with QM/MM, ONIOM, and other combined methods. I. Microiterations and constraints. J Comput Chem. 2003 Apr 30; 24(6):760-9.