Y. K. Vekilov

Dynamical stability of Fe-H in the Earth's mantle and core regions.

The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp → hcp → fcc sequence of structural transitions.

Ferromagnetism in quasicrystals : Symmetry aspects

Magnetic-group analysis of the symmetries typical of quasicrystals shows that ferromagnetism is incompatible with the icosahedral symmetry. Depending on the magnetic field direction, the icosahedral symmetry in the magnetic field is reduced to pentagonal, trigonal or rhombic symmetries.

Electronic spectrum of the three-dimensional quasi crystal

The electronic spectrum of icosahedral quasicrystal with central atom decoration of Amman-Mackay network is investigated in the tight-binding approximation. Quasicrystal is described as a structural limit of the optimal cubic approximants with increasing period. The electronic spectra for the first four optimal cubic approximants do not contain hierarchical gap structure which is typical for Cantor set of the spectrum of one-dimensional quasicrystal. At the same time the spectrum with increasing the order of approximant becomes singular on the whole energy scales.