Class I force fields

Fig. 1. Potential energy function for general class I force field.

Becke and Roussel (BR) functional, 185 Class I force fields, 41 Cyclododecane, 45 ... 

It has been suggested that the presence of cross terms (together with some other features) can provide a general way to classify force fields [Hwang et at. 1994], A class I force field was considered one which is restricted to harmonic terms (e.g. for bond stretching and... 

In molecular mechanics the force parameters of the various springs found in organic systems have to he considered. All this data is stored by the software in a file termed the force field. Attempts to produce such data began in the early 1970s. For simple molecules these are called class I force fields and for more complex systems they are termed class II. A completely generalized force field for any molecule is not really available and it is necessary to choose a force field adapted to your system from those available. 

Empirical force fields for biological macromolecules have been reviewed by Mackerell [6] and by Ponder and Case [18]. These include CHARMM, AMBER, OPES, and GROMOS. AU may be classified as a Class I force field of the general form given by Eg. (4.24)... 

Basically two ways of parametrization can be followed. Class I force fields like AMBER (Case et al. 2005) or GROMOS (2011), work with a simpler energy expression and their parameterization is based on experimental data. They find a wide application to proteins, nucleic acids, and carbohydrates, as well as their complexes. Class II force fields, e.g., the Merck Molecular Force Field (Halgren 1996) include higher order and cross terms, too they are calibrated to... 

Hagler, ]. Comput. Chem., 15, 162 (1994). Derivation of Class II Force Fields. I. Methodology and Quantum Force Field for the Alkyl Functional Group and Alkane Molecules. 

Maple JR, Hwang MJ, Stockfish TP, Dinur U, Waldman M, Ewing CS, Hagler AT, Derivation of class II force fields. I. Methodology and quantum force field for the alkyl functional group and alkane molecules, J. Comput. Chem., 15 162-182, 1994. 

Hwang, M. J. Stockfisch, T. R Hagler, A. T. Derivation of Class n force fields. 2. Derivation and characterization of a class n force field, CFF93, for the alkyl functional group and alkane molecules, J. Am. Chem. Soc. 1994,116, 2515-2525 Halgren, T. A. Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94, J. Comp. Chem. 1996,17,490-519, and subsequent papers in the same issue. 

Cartesian coordinates system for locating points in space based on three coordinates, which are usually given the symbols x, y, z or i, j, k CBS (complete basis set) an ah initio method CC (coupled cluster) a correlated ah initio method CFF (consistent force field) a class of molecular mechanics force fields CFMM (continuous fast multipole method) a method for fast DFT calculations on large molecules... 

The Canadian Task Force categorized the quality of evidence based on the type of research study. The quality of evidence was organized into three classes Class I evidence comes from procedures having at least one randomized controlled study to support them. Class II is divided into three subclasses, where II-l involves a well-designed controlled study without randomization. Class II-2 evidence comes from well-designed cohort or case-control studies, preferably carried out at more than one research setting. Class II-3 involves uncontrolled research with dramatic results (e.g., penicillin trials in the 1940s). Class III evidence includes the opinions of experts and authorities in the field based on clinical... 

In the previous chapters, we developed an approach which can be used to put the process of developing mechanistic descriptions of PES (i.e. of developing MM force fields) on a rational basis. Deductive molecular mechanics [2-4] (DMM) allows us to develop a form of the MM force fields to analyze the form of the electronic wave function relevant to the physical picture of the electronic structure of the considered class of molecules. In this chapter we apply the previously developedDMM approach to analytical derivation of the QM based form of the force fields involving the nontransition metal atoms. 

Besides issues related to the accuracy of force fields in spatially inhomogeneous systems comprising many chemically distinct components, the basic restriction related to the chemically detailed models is the rather small length and time scales that they can access. This limitation imposes severe restrictions for considering collective phenomena in amphiphilic vesicles, i.e., processes that involve large particle numbers. Typical examples include vesicle assembly, vesicle fusion, phase separation and shape transformations of multicomponent amphiphilic vesicles. For many of these processes, it is expected that the underlying atomistic details of the molecular constituents can be captured by a small number of relevant characteristics and universality classes, comprised of systems with a rather different atomistic structure, can be identified. These phenomena can be successfully investigated via minimal... 

Tetracarbonyls with Ci symmetry (see Table 16), such as a5-M(CO)4(L)2 (M = Cr, Mo, W) and M(CO)4L (M = Fe, Ru, Os L in an equatorial position in a trigonal bipyramid) are common.There are four v(CO) absorptions 2a +b +bz) and five force constants ( i, kz, kn, kzz, k z), which means that the force field is underdetermined with one degree of freedom. One of the a modes is at higher frequency and of lower intensity than the other three modes and the lower frequency a mode is always higher in frequency than the bz mode. The ordering of the low-frequency fli and the b mode is not easily predicted. Indeed, the IR spectrum of Mn(CO)4NO, which is of this class, was initially confusing since the b and low-frequency a are accidentally degenerate. ... 

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