On The Shores Of The Delaware

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Clean and As-covered zinc-blende GaN (001) surfaces: Novel surface structures and surfactant behavior

We have investigated clean and As-covered zinc-blende GaN (001) surfaces, employing first-principles total-energy calculations. For clean GaN surfaces our results reveal a novel surface structure very different from the well-established dimer structures commonly observed on polar III-V (001) surfaces: The energetically most stable surface is achieved by a Peierls distortion of the truncated (1x1) surface rather than through addition or removal of atoms. This surface exhibits a (1x4) reconstruction consisting of linear Ga tetramers. Furthermore, we find that a submonolayer of arsenic significantly lowers the surface energy indicating that As may be a good surfactant. Analyzing surface energies and band structures we identify the mechanisms which govern these unusual structures and discuss how they might affect growth properties.Comment: 4 pages, 3 figures, to be published in Appears in Phys. Rev. Lett. (in print). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Spectral Function in Mott Insulating Surfaces

We show theoretically the fingerprints of short-range spiral magnetic correlations in the photoemission spectra of the Mott insulating ground states realized in the triangular silicon surfaces K/Si(111)-B and SiC(0001). The calculated spectra present low energy features of magnetic origin with a reduced dispersion ~10-40 meV compared with the center-of-mass spectra bandwidth ~0.2-0:3 eV. Remarkably, we find that the quasiparticle signal survives only around the magnetic Goldstone modes. Our findings would position these silicon surfaces as new candidates to investigate non-conventional quasiparticle excitations.Comment: 5 pages, 4 figures. To be published in Journal of Physics: Condensed Matte

Why is the bandwidth of sodium observed to be narrower in photoemission experiments?

The experimentally predicted narrowing in the bandwidth of sodium is interpreted in terms of the non-local self-energy effect on quasi-particle energies of the electron liquid. The calculated self-energy correction is a monotonically increasing function of the wavenumber variable. The usual analysis of photo-emission experiments assumes the final state energies on the nearly-free-electron-like model and hence it incorrectly ascribes the non-local self-energy correction to the final state energies to the occupied state energies, thus leading to a seeming narrowing in the bandwidth.Comment: 9 page

Violation of particle number conservation in the it GW approximation

We present a nontrivial model system of interacting electrons that can be solved analytically in the GW approximation. We obtain the particle number from the GW Green's function strictly analytically, and prove that there is a genuine violation of particle number conservation if the self-energy is calculated non-self-consistently from a zeroth order Green's function, as done in virtually all practical implementations. We also show that a simple shift of the self-energy that partially restores self-consistency reduces the numerical deviation significantly

Hydrophobic interactions: an overview

We present an overview of the recent progress that has been made in understanding the origin of hydrophobic interactions. We discuss the different character of the solvation behavior of apolar solutes at small and large length scales. We emphasize that the crossover in the solvation behavior arises from a collective effect, which means that implicit solvent models should be used with care. We then discuss a recently developed explicit solvent model, in which the solvent is not described at the atomic level, but rather at the level of a density field. The model is based upon a lattice-gas model, which describes density fluctuations in the solvent at large length scales, and a Gaussian model, which describes density fluctuations at smaller length scales. By integrating out the small length scale field, a Hamiltonian is obtained, which is a function of the binary, large-length scale field only. This makes it possible to simulate much larger systems than hitherto possible as demonstrated by the application of the model to the collapse of an ideal hydrophobic polymer. The results show that the collapse is dominated by the dynamics of the solvent, in particular the formation of a vapor bubble of critical size. Implications of these findings to the understanding of pressure denaturation of proteins are discussed.Comment: 10 pages, 4 figure

Structure analysis of the Ga-stabilized GaAs(001)-c(8x2) surface at high temperatures

Structure of the Ga-stabilized GaAs(001)-c(8x2) surface has been studied using rocking-curve analysis of reflection high-energy electron diffraction (RHEED). The c(8x2) structure emerges at temperatures higher than 600C, but is unstable with respect to the change to the (2x6)/(3x6) structure at lower temperatures. Our RHEED rocking-curve analysis at high temperatures revealed that the c(8x2) surface has the structure which is basically the same as that recently proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)]. We found that the surface atomic configurations are locally fluctuated at high temperatures without disturbing the c(8x2) periodicity.Comment: 14 pages, 4 figures, 1 tabl

Electronic Structure of Te and As Covered Si(211)

Electronic and atomic structures of the clean, and As and Te covered Si(211) surface are studied using pseudopotential density functional method. The clean surface is found to have (2 X 1) and rebonded (1 X 1) reconstructions as stable surface structures, but no \pi-bonded chain reconstruction. Binding energies of As and Te adatoms at a number of symmetry sites on the ideal and (2 X 1) reconstructed surfaces have been calculated because of their importance in the epitaxial growth of CdTe and other materials on the Si(211) surface. The special symmetry sites on these surfaces having the highest binding energies for isolated As and Te adatoms are identified. But more significantly, several sites are found to be nearly degenerate in binding energy values. This has important consequences for epitaxial growth processes. Optimal structures calculated for 0.5 ML of As and Te coverage reveal that the As adatoms dimerize on the surface while the Te adatoms do not. However, both As and Te covered surfaces are found to be metallic in nature.Comment: 17 pages, 9 figures, accepted for publication in Phys. Rev.

Theoretical study of the (3x2) reconstruction of beta-SiC(001)

By means of ab initio molecular dynamics and band structure calculations, as well as using calculated STM images, we have singled out one structural model for the (3x2) reconstruction of the Si-terminated (001) surface of cubic SiC, amongst several proposed in the literature. This is an alternate dimer-row model, with an excess Si coverage of 1/3, yielding STM images in good accord with recent measurements [F.Semond et al. Phys. Rev. Lett. 77, 2013 (1996)].Comment: To be published in PRB Rapid. Com

Electronic structure of the MO oxides (M=Mg, Ca, Ti, V) in the GW approximation

The quasiparticle band structures of nonmagnetic monoxides, MO (M=Mg, Ca, Ti, and V), are calculated by the GW approximation. The band gap and the width of occupied oxygen 2p states in insulating MgO and CaO agree with experimental observation. In metallic TiO and VO, conduction bands originated from metal 3d states become narrower. Then the partial densities of transition metal e_g and t_2g states show an enhanced dip between the two. The effects of static screening and dynamical correlation are discussed in detail in comparison with the results of the Hartree-Fock approximation and the static Coulomb hole plus screened exchange approximation. The d-d Coulomb interaction is shown to be very much reduced by on-site and off-site d-electron screening in TiO and VO. The dielectric function and the energy loss spectrum are also presented and discussed in detail.Comment: 10 pages, 5 figure