Valence angle bending coordinate

In order to systematize the tabulation of formulas, a system of classification and of notation for the different matrix elements must be devised. First, the matrix elements are classified in terms of the general types of coordinates involved. In what follows, only two types of coordinates will appear bond stretching and valence angle bending. These types have been described in Sec. 4-2. 

In the present treatment we will pay special attention to the case where the s are valence coordinates , which consist of bond stretches, bond-angle bends, out-of-plane bends, and bond torsions.(In the more general case one could also include interpair distances for nonbonded atoms.) If the cubic and quartic interaction force constants are... 

The bonded term depends on the internal coordinates of the molecule, that is, bonds, valence angles, and dihedral angles. Accordingly, its simplest expression consists of the sum of all the terms of stretching, bending, and torsion found in a molecule. The usual expressions are briefly described. 

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