Field Parameters

We used the concept of sound velocity dispersion for explanation of the shift of pulse energy spectrum maximum, transmitted through the medium, and correlation of the shift value with function of medium heterogeneity. This approach gives the possibility of mathematical simulation of the influence of both medium parameters and ultrasonic field parameters on the nature of acoustic waves propagation in a given medium. 

The damping constant a and tire spring constant K can be written compactly in tenns of tire atomic and field parameters as... 

There are several excellent publications in the literature which compare force fields, their apphcation areas, and their pros and cons [1-5]. Available force field parameters are published in a comprehensive and very extensive form, e.g., within the R views in Computational Chemistry series [6, 7j. 

The modeling of inorganic compounds in general is gaining more and more interest [25-28]. The authors of MOMEC addressed this in a monograph describing how molecular modeling techniques can be applied to metal complexes and how the results can be interpreted [29]. The current force field parameter set is available on the author s web site. 

M. Jalaie, K. B. Lipkowitz, Published force field parameters for molecular mechanics, molecular dynamics, and Monte Carlo simulations, in Reviews in Computational Chemistry, Vol. 14, K.B. Lipkowitz, D. B. Boyd (Eds.), Wiley-VCH, New York, 2000, pp. 441-486. 

Most of the molecules we shall be interested in are polyatomic. In polyatomic molecules, each atom is held in place by one or more chemical bonds. Each chemical bond may be modeled as a harmonic oscillator in a space defined by its potential energy as a function of the degree of stretching or compression of the bond along its axis (Fig. 4-3). The potential energy function V = kx j2 from Eq. (4-8), or W = ki/2) ri — riof in temis of internal coordinates, is a parabola open upward in the V vs. r plane, where r replaces x as the extension of the rth chemical bond. The force constant ki and the equilibrium bond distance riQ, unique to each chemical bond, are typical force field parameters. Because there are many bonds, the potential energy-bond axis space is a many-dimensional space. 

Coneerted ehemieal reaetions involving simultaneous bond breaking and forming, beeause to do so would require the foree-field parameters to evolve from those of the reaetant bonding to those for the produet bonding as the reaetion proeeeds ... 

Most existing molecular mechanics studies of inorganic molecules required careful customization of force field parameters. 

Listings of references to all published force field parameters are... 

A comprehensive listing of all published force field parameters is... 

In computational chemistry it can be very useful to have a generic model that you can apply to any situation. Even if less accurate, such a computational tool is very useful for comparing results between molecules and certainly lowers the level of pain in using a model from one that almost always fails. The MM+ force field is meant to apply to general organic chemistry more than the other force fields of HyperChem, which really focus on proteins and nucleic acids. HyperChem includes a default scheme such that when MM+ fails to find a force constant (more generally, force field parameter), HyperChem substitutes a default value. This occurs universally with the periodic table so all conceivable molecules will allow computations. Whether or not the results of such a calculation are realistic can only be determined by close examination of the default parameters and the particular molecular situation. ... 

Table 1 Types and Sources of Target Data Used m the Optimization of Empirical Force Field Parameters...

Figure 4.14. Flow-field parameter distributions in front of an expanding piston. Soiution by matched asymptotic expansions by Guirao et al. compared to exact similarity solutions for various piston Mach numbers.

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