  A simple pseudopotential model is proposed, which allows the phonon spectra
and temperature dependence of the lattice heat capacity of Ir and Rh be
described with a high enough accuracy. A careful comparison of the calculated
and experimental values of the lattice heat capacity is carried out, with the
procedure of the identification of the phonon contribution to the heat capacity
and determination of the characteristics (momenta) of the phonon density of
states from the experimental values of the total heat capacity of metal at a
constant pressure being described in detail. The results of the theoretical
calculations explain, in particular, such peculiar feature of Ir and Rh,
unusual for cubic metals, as a sharp (more than by a factor of 1.5) decrease in
the effective Debye temperature with increasing termperature. The temperature
dependence of the mean square amplitude of atomic displacements in Ir and Rh
has been calculated. Basing on the band calculations the manifestation of the
Kohn singularities in the phonon spectra of Ir are discussed.
