SIMOMM: An integrated molecular orbital/molecular mechanics optimization scheme for surfaces

Reactions on surfaces are often modeled using molecular clusters which are too small to accurately represent the mechanical environment of bulk materi als. The small size of these clusters is driven by the large cost of ab ini tio quantum mechanical (QM) computational methods needed to accurately mode l chemical reactions. Hybrid computational approaches that interface quantu m mechanics with molecular mechanics (MM) methods, commonly referred to as QM/MM methods, are becoming increasingly popular for treating large systems , but these hybrid methods have not been applied to surface models. This pa per presents a QM/MM optimization scheme for modeling surfaces that is base d on the IMOMM approach of Maseras and Morokuma. The modified method, (S)ur face IMOMM, and its applications to surface chemistry are discussed.