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Lattice-Dynamical calculations on some aromatic fluoro derivatives

1976; Elsevier BV; Volume: 39; Issue: 1 Linguagem: Inglês

10.1016/0009-2614(76)85185-8

1873-4448

G. Filippini, C. M. Gramaccioli, Massimo Simonetta, Giuseppe B. Suffritti, O. Sala,

Advanced Chemical Physics Studies

Lattice-dynamical calculations according to the Born-von Kármán procedure are applied to crystals of aromatic fluoro derivatives, for which the structure is known and not disordered and the molecule can be approximately considered as 'rigid'. Force constants are obtained from lattice summations; for this purpose various semi-empirical functions for atom-atom non-bonded interaction are used, assuming F-F interactions to be equal to Ne-Ne. For most substances, a reasonable agreement with experimental data is found (lattice vibration frequencies, molecular coordinates in the cell, crystallographic temperature factors and thermodynamic functions). The only exception is 11,11-difluoro-1,6-methano annulene, for which negative eigenvalues of dynamical matrices are found for a certain region of the Brillouin zone.