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The molar volume of carbon tetrachloride is calculated as functions of temperature and pressure close to the melting point. By analyzing the experimental data for the pressure dependence of the thermal expansivity according to a power-law formula, the molar volume is calculated for the solid and liquid phases of this molecular organic compound. Our calculations show that the molar volume of the solid phase increases almost linearly as the temperature and pressure increase, so that there is no anomalous behavior close to the melting point in CCl 4. In the liquid phase, it does not vary considerably within the given pressure and temperature ranges. Our calculated molar volumes can be compared with measurements for CCl 4 under the given pressure and temperature variations.

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We study here the temperature dependence of the Raman frequencies for the overtone 2ν6 of the librational mode ν6 in phase III of NH 4 I . By using the experimental infrared frequencies of the 2ν6 mode, we predict the Raman frequencies of this overtone 2ν6 mode as a function of temperature at atmospheric pressure in phase III of NH 4 I . Our calculations indicate that the Raman frequencies of 2ν6 exhibit anomalous behavior at around 110 K (P = 0) in phase III of NH 4 I , as observed experimentally.

Spontaneous polarization and the dielectric susceptibility are calculated as a function of temperature close to the paraelectric-ferroelectric phase transition (7" c =223 K) in (NH 4 ) 2 S0 4 . This calculation is performed using a mean field model by fitting the expressions derived for the dielectric susceptibility to the experimental data for the dielectric constant at the fixed frequencies of 100, 500 and 2000 Hz in ammonium sulfate.Our calculations show that an observed first order transition can be described adequately by the mean field model given here for ammonium sulfate.