3,588 research outputs found
CO adsorption on metal surfaces: a hybrid functional study with plane wave basis set
We present a detailed study of the adsorption of CO on Cu, Rh, and Pt (111)
surfaces in top and hollow sites. The study has been performed using the local
density approximation, the gradient corrected functional PBE, and the hybrid
Hartree-Fock density functionals PBE0 and HSE03 within the framework of
generalized Kohn-Sham density functional theory using a plane-wave basis set.
As expected, the LDA and GGA functionals show a tendency to favor the hollow
sites, at variance with experimental findings that give the top site as the
most stable adsorption site. The PBE0 and HSE03 functionals reduce this
tendency. In fact, they predict the correct adsorption site for Cu and Rh but
fail for Pt. But even in this case, the hybrid functional destabilizes the
hollow site by 50 meV compared to the PBE functional. The results of the total
energy calculations are presented along with an analysis of the projected
density of states.Comment: 32 pages, 6 tables, 3 figures. (Re)Submitted to Phys. Rev. B; LDA
results added in the tables; minor changes in the tex
Freezing of Simple Liquid Metals
Freezing of simple liquid metals and the relative stabilities of competing
crystalline solids are investigated using thermodynamic perturbation theory,
the interactions between ions being modeled by effective pair potentials
derived from pseudopotential theory. The ionic free energy of the solid phase
is calculated, to first order in the perturbation potential, using classical
density-functional theory and an accurate approximation to the hard-sphere
radial distribution function. Free energy calculations for Na, Mg, and Al yield
well-defined freezing transitions and structural free energy differences for
bcc, fcc, and hcp crystals in qualitative agreement with experiment.Comment: 8 pages, 4 figures, LaTeX with elsart.st
Generalized van der Waals theory of liquid-liquid phase transitions
In the framework of the thermodynamic perturbation theory for fluids we study
how the phase diagram of an isotropic repulsive soft-core attractive potential,
where a liquid-liquid phase transition exists in addition to the standard
gas-liquid phase transition, changes by varying the parameters of the
potential. We show that existence of the liquid-liquid transition is determined
by the interplay of the parameters of the potential and the structure of a
reference liquid.Comment: 5 pages, 6 figure
Energetics of Hydrogen Chemisorbed on Cu(110): A First Principlies Calculations Study
In the current study we present a potential energy surface (PES)for atomic hydrogen chemisorbed on Cu(110)at Θ=1/8 monolayer ~ML! obtained from a plane-wave, gradient-corrected, density functional calculation. This PES is markedly different from and significantly more complex than that predicted by empirical embedded atom method (EAM) calculations. Our results, for example, suggest strongly that the hollow (HL)site is not the preferred binding site for this system. In our calculations, both the short bridge (SB)and pseudo-threefold sites are energetically more favorable than the hollow (HL)site. Energetically, we find the SB site to be slightly lower (30 meV)than the pseudo-threefold site. We also find, however, that the calculated vibrational frequencies for the pseudo-threefold site agree more closely with experimental electron energy loss data than for the SB site. In view of the relatively flat region between adjacent pseudo-threefold sites along the cross-channel [001]direction, we speculate that the hydrogen atom motion at low coverages may be two-dimensional rather than quasi-one-dimensional in character
Electronic structure of the (111) and (-1-1-1) surfaces of cubic BN: A local-density-functional ab initio study
We present ab initio local-density-functional electronic structure
calculations for the (111) and (-1-1-1) surfaces of cubic BN. The energetically
stable reconstructions, namely the N adatom, N3 triangle models on the (111),
the (2x1), boron and nitrogen triangle patterns on the (-1-1-1) surface are
investigated. Band structure and properties of the surface states are discussed
in detail.Comment: 8 pages, 12 figure
Contributors of the Summer Issue/Notes
Notes by William G. Greif, Louis Albert Hafner, William T. Huston, Maurice J. Moriarty, F. Richard Kramer, and George J. Murphy, Jr
Total energy calculation of high pressure selenium: The origin of incommensurate modulations in Se-IV and the instability of proposed Se-II
We present calculation of the high pressure crystal structures in selenium,
including rational approximants to the recently reported incommensurate phases.
We show how the incommensurate phases can be intuitively explained in terms of
imaginary phonon frequencies arising from Kohn anomalies in the putative
undistorted phase. We also find inconsistencies between the calculated and
experimental Se-II phase - the calculations show it to be a metastable metal
while the experiment finds a stable semiconductor. We propose that the
experimentally reported structure is probably in error.Comment: 4 pages 4 figure
High-efficiency quantum interrogation measurements via the quantum Zeno effect
The phenomenon of quantum interrogation allows one to optically detect the
presence of an absorbing object, without the measuring light interacting with
it. In an application of the quantum Zeno effect, the object inhibits the
otherwise coherent evolution of the light, such that the probability that an
interrogating photon is absorbed can in principle be arbitrarily small. We have
implemented this technique, demonstrating efficiencies exceeding the 50%
theoretical-maximum of the original ``interaction-free'' measurement proposal.
We have also predicted and experimentally verified a previously unsuspected
dependence on loss; efficiencies of up to 73% were observed and the feasibility
of efficiencies up to 85% was demonstrated.Comment: 4 pages, 3 postscript figures. To appear in Phys. Rev. Lett;
submitted June 11, 199
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