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The specific heat of thallium monoselenide has been investigated in /1 to 4/.The results of this works a r e in agreement with each other within the temperature range from 6 to 300 K. In /3/ an attempt has been made to explain the temperature dependence of the specific heat of TlSe by its structural peculiarities.According to /5/ there a r e two kinds of thallium ions in the crystalline structure of TlSe, monovalent T1+ and trivalent TI3+, the latter forming chains of tetrahedral bonds disposed along the tetragonal axis. The monovalent T1+ ions a r e located between the chains and provide for a weak coupling between them. In /3/ it is supposed that the arising chain structure leads to an anomaly in the temperature dependence of specific heat and reflects the peculiarities of the dynamics of highly anisotropic lattices.Previously in /6/ we have suggested a lattice dynamics model for TlSe and calculated the phonon spectrum along most of symmetrical directions in dspace inside the Brillouin zone. The parameters of this model, nine force constants, were found by fitting to eleven experimental optical phonon frequencies determined from the infrared lattice reflectivity (five frequencies) and Raman spectrum (six frequencies) /7/ a s well a s to the values of six elastic constants, determined from sound velocity measurements in various crystallographic directions /8, 9/. The calculated phonon spectrum has no appreciable anisotropy. This fact is in agreement with the values of elastic constants.Thus the interpretation of the temperature dependence of the specific heat of TlSe on the basis of the dynamics of highly anisotropic lattices is questionable. It is shown below that the observed temperature dependence of the specific heat of TlSe is quite satisfactorily explained taking into account the real phonon spectrum. The peculiaritiy of the latter is the presence of low-frequency optic a1 branches.1 ) U1. Shachbasi 5, Baku 370122, USSR.

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