Recent Publications

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  1. Title: Dipole-quadrupole interactions and the nature of phase III of compressed hydrogen

    Author(s): Kohanoff J., Scandolo S., de Gironcoli S., Tosatti E.,

    Physical Review Letters, 83, No. 20, pp. 4097-4100 (NOV 1999)

    doi: 10.1103/PhysRevLett.83.4097
    Abstract



    A new class of strongly infrared (IR) active structures is identified for phase III of compressed molecular H2 by constant-pressure ab initio molecular dynamics and density-functional perturbation calculations. These are planar quadrupolar structures obtained as a distortion of low-pressure quadrupolar phases, after they become unstable at about 150 GPa due to a zone boundary soft phonon. The nature of the II-III transition and the origin of the IR activity are rationalized by means of simple electrostatics, as the onset of a stabilizing dipole-quadrupole interaction.

  2. Title: Elasticity and mechanical instabilities of diamond at megabar stresses: implications for diamond-anvil-cell research

    Author(s): Ji-Jun Zhao, Scandolo S., Kohanoff J., Chiarotti G.L., TosattiE.,

    Applied Physics Letters, 75, No. 4 (JUL 26 1999)

    doi: 10.1063/1.124424
    Abstract



    We present first-principles calculations of the stress–strain curves for diamond under nonhydrostatic tetragonal compression, in the regime of operation of diamond-anvil cells (DACs). We provide a parametrization of the stress components as a function of strain, which is potentially useful for the controlled design of DACs. A stability analysis shows that a tetragonal-shear mechanical instability sets in in diamond when sigmaz – sigmar = 200 GPa, where sigmaz and sigmar are the axial and radial components of the stress, respectively.

  3. Title: The puzzling stability of monotaomic gold wires

    Author(s): Torres J.A., Tosatti E., Dal Corso A., Ercolessi F., Kohanoff J., di Tolla F.D., Soler J.M.,

    Surf. Science, 426, No. L441 (1999)

    Abstract