Ab initio phonon dispersion relations of $\mathsf{\alpha}$-Ga

We present the ab initio phonon dispersion relations of -Ga. The calculations are carried out within density functional perturbation theory by using either norm-conserving pseudopotential and 4s and 4p electrons in the valence or ultrasoft pseudopotential and 3d electrons in the valence as well. The inclusion of 3d electrons in the valence turned out to be necessary to better reproduce the experimental frequencies of the stretching modes of the Ga₂ dimers present in the -Ga structure.Received: 29 July 2003, Published online: 19 November 2003PACS: 63.20.Dj Phonon states and bands, normal modes, and phonon dispersion - 71.15.Nc Total energy and cohesive energy calculations - 71.15.Mb Density functional theory, local density approximation, gradient and other corrections     

An $\mathsf{\epsilon}$-expansion for small-world networks

I construct a well-defined expansion in for diffusion processes on small-world networks. The technique permits one to calculate the average over disorder of moments of the Greens function, and is used to calculate the average Greens function and fluctuations to first non-leading order in , giving results which agree with numerics. This technique is also applicable to other problems of diffusion in random media.Received: 28 July 2004, Published online: 14 December 2004PACS: 89.75.Hc Networks and genealogical trees 64.60.Ak Renormalization-group studies of phase transitions     

Intensity ratios of mesonic x-ray linesK_{\alpha _1 } , K_{\alpha _2 } andL_{\alpha _1 } , L_{\beta _2 }

Intensity ratios ofμ-mesonic x-rays in some heavy elements are discussed. Intensity ratios of the \(K_{\alpha _1 } /K_{\alpha _2 } \) and \(L_{\alpha _1 } /L_{\beta _2 } \) lines have been calculated for²⁰⁶Pb,²⁰⁹Bi and²³⁸U with relativistic wavefunctions and retardation effect. Though for a refined calculation, it is necessary to take into consideration several features that are peculiar to mesonic atoms, the present calculations have shown that the observed intensity ratios of mesonic x-rays are not anomalous.     

Scaling of the spin stiffness in random spin- \frac{\mathsf 1}{\mathsf 2} chains

In this paper we study the localization transition induced by the disorder in random antiferromagnetic spin- chains. The results of numerical large scale computations are presented for the XX model using its free fermions representation. The scaling behavior of the spin stiffness is investigated for various disorder strengths. The disorder dependence of the localization length is studied and a comparison between numerical results and bosonization arguments is presented. A non trivial connection between localization effects and the crossover from the pure XX fixed point to the infinite randomness fixed point is pointed out.Received: 6 February 2004, Published online: 12 August 2004PACS: 75.10.Jm Quantized spin models - 75.40.Mg Numerical simulation studies - 05.70.Jk Critical point phenomena - 75.50.Lk Spin glasses and other random magnets