Towards more realistic computational modeling of homogenous catalysis by density functional theory: combined QM/MM and ab initio molecular dynamics

The combined quantum mechanics/molecular mechanics (QM/MM) and the ab initi o molecular dynamics methods (AIMD) are fast emerging as viable computation al molecular modeling tools. Both methods allow for the incorporation of ef fects that are often ignored in high level calculations, but may be critica l to the real chemistry of the simulated system. In the combined QM/MM meth od part of the system, say the active site, is treated quantum mechanically whereas the remainder of the system is treated with a faster molecular mec hanics force field. This allows high level calculations to be performed whe re the effects of the environment are incorporated in a computationally tra ctable manner. With the ab initio molecular dynamics methods, the system is simulated at a finite temperature with no empirical force field. Rather, t he forces at each time step are determined with a full electronic structure calculation at the density functional level. Thus, simulations of chemical reactions can be performed where finite temperature effects are realistica lly represented. In this paper a brief introduction to both methods is give n. The methods are further demonstrated with specific applications to model ing homogenous catalytic processes at the molecular level. These applicatio ns are our latest efforts to build more realistic computational models of c atalytic systems at the density functional level. (C) 1999 Elsevier Science B.V. All rights reserved.