Force fields amorphous state

For the simulation of amorphous polymers in the solid state, these limitations are not very restrictive, as most commercially important polymers display a simple bonding situation that is well parametrized by modern force fields. They contain mostly atoms of the first two rows of the periodic system and can be mostly treated by non-relativistic Hartree-Fock level calculations. It is emphasized, however, that the above requirements should be checked for any system in advance. 

Despite the tremendous progress made in this field, there is still a severe drawback. The quantum chemistry developed by theoretical chemists tools are primarily suited for isolated molecules in vacuum or in a dilute gas, where intermolecular interactions are negligible. Another class of quantum codes that has been developed mainly by solid-state physicists is suitable for crystalline systems, taking advantage of the periodic boundary conditions. However, most industrially relevant chemical processes, and almost all of biochemistry do not happen in the gas phase or in crystals, but mainly in a liquid phase or sometimes in an amorphous solid phase, where the quantum chemical methods are not suitable. On the one hand, the weak intermolecular forces,... 

A relatively new field called supramolecular chemistry has been developed over the last three decades. Supramolecular assemblies and supramolecular polymers differ from macromolecules, where the monomeric units are covalently linked. In a supramolecular polymer, the monomeric units self-assemble via reversible, highly directional, noncova-lent interactions. These types of bonding forces are sometimes called secondary interactions. Hydrogen bonding is the secondary force most utilized in supramolecular chemistry, but metal coordination and aromatic tt-tt electronic interactions have also been used. From a materials standpoint, supramolecular assemblies are promising because of the reversibility stemming from the secondary interactions. The goal is to build materials whose architectural and dynamical properties can respond reversibly to external stimuli. Solid phases are prepared by self-assembly from solution. In the solid-state, supramolecular polymers can be either crystalline or amorphous. 

The properties of equations such as (3) and (4) which are not allowed by RMT are understood satisfactorily only in the relatively uninteresting linear case where, for example, rise and fall transients mirror each other as exponentials. When this frontier is crossed, the applied field strength is such that it is able to compete effectively with the intermolecular forces in liquids. This competition provides us with information about the nature of a molecular liquid which is otherwise unobtainable experimentally. This is probably also the case for internal fields, such as described by Onsager for liquids, for various kinds of intmial fields in int ated computer circuits, activated polymers, one-dimensional conductors, amorphous solids, and materials of interest to information tedmology. The chapters by Grosso and Pastori Parravidni in this volume describe with the CFP some important phenomena of the solid state of matter in a slightly different context. 

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