Modern Physics Letters B

The phenomenon of propagation of a stress field through complex 3d polycrystalline materials along the grain boundaries performing very slow random motion is studied. After applying the Hall–Petch coupling relation it turns out that the relaxation process proceeds in time anomalously. As a consequence, a fractional evolution equation of order one half for the relaxation function is postulated and its solutions are presented. Interpretations of the process in terms of the diffusion on a comb-like structure (antipersistent Random Walk with d_w=4 and/or the generalized Gauss–Kolmogorov (in)homogeneous turbulence scenario with the Hurst exponent of H = 1/4 are proposed.

Electronic structures of simple cubic (sc) Na₂CsC₆₀ and body-centered-cubic (bcc) K₆C₆₀ are studied using the tight-binding recursion method. We find that the orientational disorder modifies the electronic states of sc Na₂CsC₆₀ significantly. The ground state of K₆C₆₀ is found to be insulating with a gap of 0.20 eV. The valence electrons of the alkali-metal atoms in both Na₂CsC₆₀ and K₆C₆₀ are almost completely transferred to the lowest unoccupied bands of the C₆₀ molecular solid. The strength of the interaction between the alkali-metal atom and the C₆₀ molecule is estimated.

The optical absorption spectra of zigzag fullerene tubes have been studied by using the extended Su–Schrieffer–Heeger model with the Coulomb interaction included. The numerical results indicate that the carbon number and the Coulomb interaction have great effects on the optical absorption spectra.

The effect of the central cell correction on the binding energies of shallow donors in a spherical GaAs-Ga_1-xAl_xAs quantum dot is studied. The effective-mass approximation within a variational scheme is adopted and central cell corrections are calculated by using a Coulomb potential modified with an adjustable parameter. For small values of the radius of the dot large corrections are obtained for the shallow donors studied.

In this paper we discuss structural and dynamical properties of nano-clusters. The study is based on molecular dynamics calculations. In particular, the behavior of the following functions have been studied: single-particle distribution function, velocity autocorrelation function and the generalized phonon density of states (PDOS). The calculations have been done for krypton since for this material a realistic pair potential is available (Barker et al. potential). In order to have more informations about the nano-cluster properties, we also performed molecular dynamics calculations for the bulk. The comparison of the bulk results with the nano-cluster results shows that the shift of the cluster PDOS to low frequencies, caused from the different number of particles.