The ONIOM method: its foundation and applications to metalloenzymes and photobiology

The ONIOM (our Own N-layer Integrated molecular Orbital molecular Mechanics) method is one of the most popular, successful, and easily-to-implement hybrid quantum mechanics/molecular mechanics (QM/MM) methods to treat complex molecular systems. Hybrid QM/MM methods take advantage of the high accuracy of QM methods and the low computational cost of MM methods. One key feature of the ONIOM method is a simple linear extrapolation procedure, which allows the ONIOM method to be further extended to two-layer ONIOM(QM1:QM2), three-layer ONIOM(QM1:QM2:MM), and, in principle, any n-layer n-level-of-theory methods. Such hierarchical features of the ONIOM method are unique among the hybrid QM/MM methods. This review article provides an overview of the theoretical foundation and recent development of the ONIOM method. Some of its recent applications to metalloenzymes and photobiology will also be highlighted. Prospective ONIOM development for more realistic simulations on the complex systems will be discussed finally. (c) 2011 John Wiley & Sons, Ltd.