Polarization force field treatment

The MM2 program [52] is by faf the most widely used force field program in the area of hydrocarbon or moderately polar molecules and numerous publications have demonstrated its usefulness. Still the anomeric center had not until recently been properly defined by the force field parameters. Now there are parameters available which include the proper treatment of acetal fragments and hence reproduce the anomeric as well as the exo anomeric effect accurately [53]. Due to the full optimization of the geometry the MM2 program can treat only a limited number of atoms. 

Another important property of thiepine is the equilibrium between thiepine (1) and its valence isomer, benzene episulflde (9). Benzene episuliides are found to be so unstable that they can not be detected hence theoretical treatment should provide helpful information. MNDO molecule force field calculations of the zero point energy, potential energy, and thermodynamic parameters for the valence tautomerization of benzene episulflde (9) and thiepine (1) show that (9) is more stable than (1) both in the gas phase and in polar media (Equation (1)). The equilibrium is shifted towards (1) in polar media. The vapor phase inversion barrier for (1) is 3-5 kJ mol , and is reduced to zero by polar solvents <83MI 903-01 >. 

Carbonization is another PSM strategy. This approach fabricates porous carbon by thermal treatment of POFs with or without a template. In the carbonization process, chemical bond breaking accompanies the formation of a novel porous framework, as well as shrinking of the pore size. Generally, the carbonized porous material exhibits strong host-guest interactions due to the overlapped force field and the enhanced polarity. ... 

An alternative approach is to combine QM and MM methods such that the reacting system (or the active site in an enzyme) is treated explicitly by a quantum mechanical method, while the surrounding environmental solvent molecules (or amino acids), which constitute the most time-consuming part in the evaluation of the potential energy surface, are approximated by a standard MM force field. " Such a method takes advantage of the accuracy and generality of the QM treatment for chemical reactions - and of the computational efficiency of the MM calculation.Because the reactant electronic structure and solute-solvent interactions are determined quantum mechanically, the procedure is appropriate for studying chemical reactions, and there is no need to parameterize potential functions for every new reaction. Furthermore, the solvent polarization effects on the solute are naturally included in the... 

Buckingham and Pople gave a more complete treatment than Stockmayer s of the interaction between two molecules having non-central force fields. Their treatment allows not only for dipole-dipole interaction but also for dipole-quadrupole, quadrupole-quadrupole, dipole-induced dipole, steric, anisotropic, and other effects. An important feature of the Buckingham-Pople procedure is that the various integrals needed can be calculated from a master table that they give. Buckingham and Pople applied their method to four polar compounds for which values of the dipole moment and the polarizability were known, and used B(T) to... 

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