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To investigate the lattice dynamics of potassium halides a newly proposed 7-parameter bond-bending force model (BBFM) is used. The total potential energy of the system incorporates the short-range forces (radial+-bond-bending) as well as the long range Coulombic interactions. The 7 parameters employed in the present treatment are determined by making use of the experimental values of three elastic constants, four critical point phonon frequencies and the lattice equilibrium condition. The model has been applied to calculate the phonon dispersion relations, phonon density of states and the Debye-characteristic termperatures (θ D ) of KCl, KBr, and KI. Theoretical results have been compared with the available experimental data. It is observed that the agreement between theory and experiment is very good and thus gives a confidence in this approach. The remarkable features pertaining to the physical significance of the model have been discussed.

Phonon dispersion relations for compounds having zinc blende structure have been studied in the framework of dynamic model, which takes into account the covalent nature of atomic bonds. The calculated dispersion curves for GaAs and InSb along three symmetry directions [100], [110] and [111] in K-space are found to be in good agreement with the measured inelastic neutron scattering data.

An approximate estimate of critical point phonon frequencies has been made for ZnTe and CdTe in the frame-work of the new dynamic model [J. Phys. Soc. Jpn. 54 (1985) 617]. Maxima in the infrared absorption and/or Raman scattering experiments have been tentatively assigned in terms of lattice dynamical critical phonons. The calculated phonon frequencies show a reasonably satisfactory agreement with the available optical and neutron scattering data.

The unpaired elastic force model (EFM) developed by Kushwaha and Kushwaha 1) has been extended to study the lattice dynamics of solid Neon (Ne) and Xenon (Xe). The application of the model has been made to calculate the phonon frequencies of Ne and Xe at all the irreducible points of the first Brillouin Zone. Use thereof has been made to calculate the lattice heat capacities and Debye characteristic temperatures in the temperature range 4–24 K and 4–100 K for Ne and Xe respectively. The calculated values of phonon frequencies along the three symmetry directions [100], [110], and [111], heat capacities and the Debye characteristic temperatures have been compared with the recent available experimental data. The merits and demerits of the model have been widely discussed.

The root mean square amplitudes of the constituent atoms in II–VI and III–V binary compound semiconductors as a function of temperature have been calculated using new dynamic model (R. K. Ram and S. S. Kushwaha: J. Phys. Soc. Jpn. 54 (1985) 617.). The calculated results have been compared with the available experimental data. The melting criteria of these compounds have been also explained.