Determination of the thermodynamic functions of lead carbonate on the basis of the calculation of vibrational states

The force constants of bond angles and bonds and parameters of the interatomic potential for the natural carbonate cerussite were determined from the valence force field calculation of the vibrational states of its crystal structure. The initial force constants were calculated by the semiempirical PM5 method using the MOPAC quantum-chemical program package. As the criterion of adequacy of calculations, the consistency between the simulated IR and Raman spectra and the experimental spectra of the compound was used. The heat capacity of lead carbonate as a function of temperature was calculated based on the theory of crystal lattice dynamics and by quantum-chemical methods. The best fit to the experimental data was provided by the semiempirical PM5 method. From the calculated heat capacities, the entropy values of the compound were found.