Correlation and prediction of thermodynamic data for oxide and silicate minerals

Often one needs to estimate heat capacities and related properties such as the entropy for a particular material through interpolation, extrapolation, or comparison with data for related materials. A scheme is discussed to pe rform such estimates, focusing on the vibrational entropy. At intermediate and high temperatures, the entropy depends only on the logarithmic average over the phonon frequencies. This average can be factorized, so that the at omic masses separate from the interatomic force constants. Thus, one can ac count for the mass effect in the vibrational entropy and get a remaining qu antity which depends only on the force constants, i.e., on the electronic s tructure, and shows a strong regularity when chemically similar materials a re compared. In the framework of these ideas, estimates based on an additiv ity rule for the entropy of a complex system in terms of the entropies of t he constituents. and also relations between the vibrational entropy and sou nd velocities, are discussed. Oxide and silicate minerals are used as examp les.