Molecular force fields and

This article reviews progress in the field of atomistic simulation of liquid crystal systems. The first part of the article provides an introduction to molecular force fields and the main simulation methods commonly used for liquid crystal systems molecular mechanics, Monte Carlo and molecular dynamics. The usefulness of these three techniques is highlighted and some of the problems associated with the use of these methods for modelling liquid crystals are discussed. The main section of the article reviews some of the recent science that has arisen out of the use of these modelling techniques. The importance of the nematic mean field and its influence on molecular structure is discussed. The preferred ordering of liquid crystal molecules at surfaces is examined, along with the results from simulation studies of bilayers and bulk liquid crystal phases. The article also discusses some of the limitations of current work and points to likely developments over the next few years. 

The various types of successful approaches can be classified into two groups empirical model calculations based on molecular force fields and quantum mechanical approximations. In the first class of methods experimental data are used to evaluate the parameters which appear in the model. The shape of the potential surfaces in turn is described by expressions which were found to be appropriate by semiclassicala> or quantum mechanical methods. Most calculations of this type are based upon the electrostatic model. Another more general approach, the "consistent force field method, was recently applied to the forces in hydrogen-bonded crystals 48> 49>. 

The molecular dynamics unit provides a good example with which to outline the basic approach. One of the most powerful applications of modem computational methods arises from their usefulness in visualizing dynamic molecular processes. Small molecules, solutions, and, more importantly, macromolecules are not static entities. A protein crystal structure or a model of a DNA helix actually provides relatively little information and insight into function as function is an intrinsically dynamic property. In this unit students are led through the basics of a molecular dynamics calculation, the implementation of methods integrating Newton s equations, the visualization of atomic motion controlled by potential energy functions or molecular force fields and onto the modeling and visualization of more complex systems. 

The most time-consuming and rigorous methods are based on molecular force fields and involve slow gradual transformations between the states of interest using either molecular dynamics (MD) or Monte Carlo (MC) simulations for generating ensemble averages.291... 

Molecular force fields and chemical shift pseudo-forces 75... 

The nonbonded interactions and the torsional potentials are perhaps the most crucial and difficult-to-obtain portions of any molecular force field, and we shall discuss them at length in later sections. 

The late Pierre Claverie was one of the most influential French researchers in the field of intermolecular interactions. His work dedicated to the foundation of molecular force fields and their links with quantum chemistry was truly visionary. Since about 1970, Claverie has pointed out the importance of taking polarization effects into account in molecular mechanics, and he proposed the concept of self-encased different levels of computations regarding solvent effects, thereby showing the road to the present development of hybrid quantum mechanics/molecular mechanics (QMVMM) methods. 

Cook, R. L, F. C. De Lucia, and P. Helminger, Molecular force field and structure of water Recent microwave results. J. Mol. Spectrosc., 1974. 53 62-76. 

Figure 6.1 The scheme for the bottom-up multiscale simulation method, in which the quantum chemistry method, including first-principle calculations and DFT, was used to obtain the binding energy between gas molecules and COF materials. By fitting the binding energy into the molecular force fields and further inputting the force fields into a statistical mechanics-based molecular simulation, we can predict adsorption properties of COF materials. This bottom-up multiscale method spans three scales, including the electronic scale, the molecular scale, and the macroscale.

N. Neto, G. Taddei, S. Califano, and S.H. Walmsley, Lattice dynamics of molecular crystals using a molecular force field and an intermolecular potential function with application to the atom-atom model. Mol. Phys. 31 457 (1976). 

Visualising (intra)molecular force-fields and submolecular structure... 

Recent day, quantum mechanics becomes very popular to explain the mechanistic features of bio-active molecules. There are several quantum chemical descriptors through which we can predict reaction mechanism and as well as stmcture activity relationship of munerous bioactive molecules. A number of excellent reviews have been pubhshed on the application of quantum chemical descriptors in SAR/SPR studies [24—26]. To determine the equilibrium geometry, the molecular force field and to compute the quantum mechanical descriptors of the dmg molecules, some suitable quantum mechanical method are invoked [27]. 

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