By using the methods of acoustic emission and neutron-structure analysis, the effect of pressurep on low-temperature phase transitions in Li and Na is investigated. In Li, within the investigated interval ofp S 3 GPa, the transition temperature rises with pressure, and the low-temperature phase has a 9R structure. In Na, on the contrary, pressure suppresses the transition, so that it disappears even a t p = 0.1-0.2 GPa but the 9R phase is the low-temperature one too. The shape of acoustic emission signals suggests the presence of pre-transition phenomena and differences in the kinetics of transitions in Li and Na. Calculations performed explain the difference in the influence of pressure on structural stability of Li and Na by the effect of proximity of the Fermi level to peaks in the electronic density of states, which appears under pressure in Li but is absent from Na. The same effects account for a pre-martensitic softening of the shear constant, observed under compression of Li.

The possibility is discussed of describing lattice properties of iridium in terms of pseudopotential perturbation theory with allowance for second and third order. Values of pseudopotential parameters are proposed which provide a good description of the lattice properties of iridium under zero pressure, the contributions of the three-ion forces being small. The total energy, pressure, elastic moduli, Debye temperature, low-temperature Gruneisen parameter, pairwise potentials, and also effective solid sphere packing parameters are calculated. In addition, by invoking molecular dynamic methods, the vacancy formation and migration energies and the stacking fault energies are computed. The electron energy spectrum and group velocity calculations suggest that the electron density of states curve of Ir exhibits no van Hove singularities near the Fermi level, a fact which apparently accounts for the successful description of lattice properties in terms of the pseudopotential perturbation theory.

Many slow electrons in the field of a residual ion are shown to have Wannierlike stationary configurations. Solutions of the Schrodinger equation in this limited region of space are obtained and applied to the investigation of the cross section for multiple ionization near threshold. Numerical results are presented for double escape in several spin and angular momentum states and for triple escape in the *S and 4S states.

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