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** Consistent valence force field **

** Consistent valence force field CVFF) **

** Generalized valence force field **

** Simplified general valence force field **

** Spectroscopic general valence force field **

** Valence force field potentials **

Some authors use the terms valence force field and Urey-Bradley force field in the sense of molecular mechanics. The former refers to the force field taking no explicit account of 1,3-interactions, which are intended in the latter. [Pg.120]

A. Serrallach, R. Meyer, and H. H. Giinthard, Methanol and deuterated species Infrared data, valence force field, rotamers, and conformation. J. Mol. Spectrosc. 52, 94 129 (1974). [Pg.54]

We refer to models where we write the total potential energy in terms of chemical endties such as bond lengths, bond angles, dihedral angles and so on as valence force field models. [Pg.38]

IR absorptions of these species were assigned to fundamental modes by comparison with the spectra of stable perfluoroorganic compounds. Normal coordinate analysis of the perfluoroethyl radical was performed and the valence force field of C2F5 was calculated (Snelson et al., 1981). [Pg.34]

From the above example it is apparent that there may be (and usually are) more unknown force constants than observed frequencies. If no additional sources of data are available, it is necessary to make some assumptions to simplify the force field. Often all or some of the off-diagonal elements in the F matrix [Eq. (63)] are neglected, leading to the so-called valence force field (VFF) or modified valence force field (MVFF), respectively. [Pg.123]

In the construction of the matrix F of Eq. (63), the symmetrical equivalence of the two O-H bonds was taken into account. Nevertheless, it contains four independent force constants. As the water molecule has but three fundamental vibrational frequencies, at least one interaction constant must be neglected or some other constraint introduced. If all of the off-diagonal elements of F are neglected, the two principal constants, f, and / constitute the valence force field for this molecule. However, to reproduce the three observed vibrational frequencies this force field must be modified to include the interaction constant [Pg.121]

In a different approach to this problem, Brenner and Garrison used molecular dynamics to examine the chemical mechanisms which lead to reordering of the atom-pairing reconstruction during atom deposition . This simulation incorporated a dissociative valence-force field potentiaF and consisted essentially of a high-temperature anneal of monolayers of silicon atoms which had been deposited on a silicon (001) reconstructed surface. [Pg.321]

There are some systems for which the default optimization procedure may not succeed on its own. A common problem with many difficult cases is that the force constants estimated by the optimization procedure differ substantially from the actual values. By default, a geometry optimization starts with an initial guess for the second derivative matrix derived from a simple valence force field. The approximate matrix is improved at each step of the optimization using the computed first derivatives. [Pg.47]

The absence of overlapping of bands of various matrix-isolated compounds and the possibility of freezing highly reactive intermediates make this method very convenient for the direct study of reaction mechanisms. Additionally, direct IR spectroscopy of intermediates allows estimation of important structural parameters, e.g. valence force fields, which show the character of bonds in these species. [Pg.6]

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** Consistent valence force field **

** Consistent valence force field CVFF) **

** Generalized valence force field **

** Simplified general valence force field **

** Spectroscopic general valence force field **

** Valence force field potentials **

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