  The crystal structure, phonon spectrum, and elastic constants of a series of
rare-earth germanates (including yttrium germanate R2Ge2O7 (R = Tb-Lu, Y)) with
a tetragonal structure have been ab initio calculated within the density
functional theory. The frequencies and types of fundamental vibrations and the
intensities of IR and Raman modes are determined. The degrees of participation
of ions in each mode are determined by analyzing the displacement vectors
obtained as a result of the ab initio calculations. The calculations have been
performed for the first time; there are no corresponding experimental data for
the entire series of compounds (except for the IR and Raman spectra of yttrium
germanate). The performed calculations made it possible to interpret and
supplement the known data in the literature on IR and Raman spectra of yttrium
germanate Y2Ge2O7.
