Cell model and quasti-harmomc cakulatrons are carned out for five chlorobenzene crystals usmg a semi-emplncal atom-atom approxlmahon to Lhe mtermolecular interacuon potential The cell model results show good agreement with expcnment, except for 1,2,4,5tetrachlorobenzene where the quasi-harmonic approxlmafion proves more appropnate I-Introduction In previous papers [ 143, a new method has been suggested for calculating, on a microscoprc level, the thermodyitamic properties of an organic molecular crystal. The method combines the so-called cell model [5], as a statistical-mechanical basis, with the atomatom potential method [6], as an approximation to the interrtolecular interaction potential. The cell model calculations have been performed for a number of hydrocarbon crystals [ 14) and shown excellent agreement wrth experrment. An extension of the calculations to chlorinated benzene crystals requires a knowledge of atom-atom potentials describing the interactlons of chlorme atoms. In a recent work [7], three potential models for the Cl...Ci interactions were tested, all being of the Buckingham (exp-6) type, but wrth drfferent potential parameters. The most appropriate was found to be the parameter set derived by Bates and Busmg [S] from the crystal structure and sublimation heat of hexachlorobenzene. This paper provides a further test for the model and particular parameter set. The calculations are carrred out for a series of chlorinated benzenes, including chlorobenzene, 1,4_dichlorobenzene, 1,3,5-trichlorobenzene, 1,2,4,5tetrachlorobenzene and hexachlorobenzene_ The cell model results are compared with experiment and also with quasiharmonic results obtained via solution of the latticedynamical problem. 176 2. The method of calculation