Chemical physics of solids and their surfaces Volume 7; A by M W Roberts; J M Thomas; R I Bickley

By M W Roberts; J M Thomas; R I Bickley

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Extra resources for Chemical physics of solids and their surfaces Volume 7; A review of the literature published up to mid-I 977

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Scheraga, Proc. Nut. Acad. , 1967, 58,420. J. Bernstein and A, T. Hagler, J. Amer. Chem. , 1978, 100, 673. J. M. Adams and S. Ramdas, to be published. S. Ramdas, W. Jones, J. M. Thomas, and J. P. Desvergne, Chem. Phys. Letters, 1978,57,468. Chemical Physics of Solids and their Surfaces 42 CI 0 Figure 2 (a) 9,lO Diphenyl anthracene; (b) 1,s Dichloro unthracene; (c) Pyrene Pyrene. The low temperature crystal structure of pyrene (Figure 2c) is another example. Pyrene undergoes a phase transition on cooling from room temperature to about 120 K 36 with no change in the space group but with slight modifications of the a, b, and p parameters.

The most exhaustive calculation reported so far is that of Williams l 3 where 130 observational equations from 18 hydrocarbon crystal structures were used for the fitting procedure on the potentials. It was again found that the same potentials could be used for both unsaturated and saturated hydrocarbons. Further, it was also shown that the dispersive attraction is better described by the atom-centred rather than the bond-centred interactions. A set of such derived non-bonded potential parameters are listed in Table 1;also listed there, are some of the parameters estimated by other workers employing similar fitting procedures.

Atom-atom potentials have been widely tested for their transferability characteristics in the case of hydrocarbons and in some substituted materials. With known cell volume and the space group, the packing of molecules in crystals has been accurately predicted in most cases within an overall error of 2-3%. The method is most successful when the constituent molecules are rigid like the fused ring systems. In cases where the molecules are not rigid, the same non-bonded interaction potentials are used in estimating the intramolecular contributions to the total potential energy for subsequent minimization with respect to additional internal variables.

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