The simplest anharmonic characteristics of Ir and Rh are discussed in the framework of a previously developed simple pseudopotential model which describes the elastic moduli, phonon spectra and the lattice heat capacity in the harmonic approximation of these metals succesfully. The microscopic Gruneisen parameters, the dependences of the elastic moduli on pressure, the coefficient of thermal expansion and the equations of state at the finite temperatures have been calculated. The ab initio calculations of the energy-band structure and the equation of state for Ir at T = 0 have been done to test the model for adequacy at high pressures. The values of different contributions (zero-point oscillations, quasiharmonic, etc.) in the considered thermodynamic characteristics of Ir and Rh are discussed. §1. IntroductionAs it is stated in the literature (Gornostyrev et al 1994, Ivanov et al 1994, Katsnelson et al 1996 referred to as I), Ir and its analogue Rh are set off from other FCC metals because of some distinctive features of their physical properties: unusual deformation-induced failure, peculiar defect structure, specific temperature dependence of the effective Debye temperature, etc. Moreover, the situation is not trivial because in the case of Ir, unlike the most, if not all of the other FCC metals a rather broad range of properties (elastic moduli, phonon spectra and lattice heat capacity) can be described in terms of a simple pseudopotential model (see I and references therein). Even in sp-metals the situation is less favorable: to describe the elastic moduli of Ca allowance must be made for the singular contributions to energy which result from the proximity of the Fermi surface and the faces of the Brillouin zone (Katsnelson et al 1990), whereas for Al it is necessary to take into account the contributions of three body forces. Nevertheless, in describing the phonon spectra of Al it is impossible to attain an accuracy 1