Molecular mechanics potentials, direct systems

The proper representation of solvents in quantum chemical (QC) calculations is of crucial importance for the future success of QC because the vast majority of technical and biological chemistry takes place in fluid systems, while QC has been developed for isolated molecules for 40 years. Because of the extremely large number of molecules necessary for a realistic description of a solvent environment and the exponential increase of the costs of QC calculations with increasing size of the system, a direct extension of QC to such systems appears to be impossible in general, although first steps towards that goal have been made by the Car-Parrinello method (see Combined Quantum Mechanical and Molecular Mechanical Potentials and Combined Quantum Mechanics and Molecular Mechanics Approaches to Chemical and Biochemical Reactivity). Mixed classical quantum methods could... 

Direct dynamics is applicable to large molecular systems, but a lower level of electronic structure may be required as well as a blend of direct dynamics and analytic potential energy functions. This latter technique, often called quantum mechanical/molecular mechanical (QM/MM) direct dynamics [377], has been used to simulate SID unimolecular dynamics associated with protonated glycine ions, NH3CH2COOH [(gly-H)+j, colliding with a hydrogenated diamond 111 surface [378]. The potential energy for the system is represented by... 

Contrary to the generalized approach already presented, models describing the adhesion between a polymer well defined at a molecular level and another, equally molecularly well-defined substrate also exist. These are models in which molecular mechanics and dynamics are applied in their more accepted role described in the Introduction. It must be realized that such models derive from a need different from what has prompted the development of the generalized models already described. They stem from the need to solve some applied problem of adhesion or to upgrade the performance of some adhesive systems in situations where the use of an experimental method would take too long, or is not able to give any clear results. It is for this reason that such models need to use the most precise and well-defined information possible or available on the molecules involved as well as using the sets of potential functions which describe in the most accurately conceptual manner the molecular behavior of the chemical species involved all the research work that uses this approach is then applied to real case, not to idealized models, and is of considerable sophistication. Furthermore, all this type of research work is most commonly supported by direct or indirect experimental results... 

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