5,309 research outputs found
Important role of alkali atoms in A4C60
We show that hopping via the alkali atoms plays an important role for the t1u
band of A4C60 (A=K, Rb), in strong contrast to A3C60. Thus the t1u band is
broadened by more than 40 % by the presence of the alkali atoms. The difference
between A4C60 and A3C60 is in particular due to the less symmetric location of
the alkali atoms in A4C60.Comment: 5 pages, revtex, 2 figures, submitted to Phys. Rev. B more
information at http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene
Structure and energetics of Si(111)-(5x2)-Au
We propose a new structural model for the Si(111)-(5x2)-Au reconstruction.
The model incorporates a new experimental value of 0.6 monolayer for the
coverage of gold atoms, equivalent to six gold atoms per 5x2 cell. Five main
theoretical results, obtained from first-principles total-energy calculations,
support the model. (1) In the presence of silicon adatoms the periodicity of
the gold rows spontaneously doubles, in agreement with experiment. (2) The
dependence of the surface energy on the adatom coverage indicates that a
uniformly covered phase is unstable and will phase-separate into empty and
covered regions, as observed experimentally. (3) Theoretical scanning tunneling
microscopy images are in excellent agreement with experiment. (4) The
calculated band structure is consistent with angle-resolved photoemission
spectra; analysis of their correspondence allows the straightforward assignment
of observed surface states to specific atoms. (5) The calculated activation
barrier for diffusion of silicon adatoms along the row direction is in
excellent agreement with the experimentally measured barrier.Comment: 11 pages, 7 figures, also available with higher-resolution figures
from http://cst-www.nrl.navy.mil/users/erwin/ausi111.v5.pd
Commensurate and modulated magnetic phases in orthorhombic A1C60
Competing magnetically ordered structures in polymerized orthorhombic A1C60
are studied. A mean-field theory for the equilibrium phases is developed using
an Ising model and a classical Heisenberg model to describe the competition
between inter- and intra-chain magnetic order in the solid. In the Ising model,
the limiting commensurate one-dimensional and three-dimensional phases are
separated by a commensurate three-sublattice state and by two sectors
containing higher-order commensurate phases. For the Heisenberg model the
quasi-1D phase is never the equilibrium state; instead the 3D commensurate
phases exhibits a transition to a continuum of coplanar spiral magnetic phases.Comment: 11 pages REVTeX 3.0 plus 4 figures appende
Floppy modes and non-affine deformations in random fiber networks
We study the elasticity of random fiber networks. Starting from a microscopic
picture of the non-affine deformation fields we calculate the macroscopic
elastic moduli both in a scaling theory and a self-consistent effective medium
theory. By relating non-affinity to the low-energy excitations of the network
(``floppy-modes'') we achieve a detailed characterization of the non-affine
deformations present in fibrous networks.Comment: 4 pages, 2 figures, new figure
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