1,721,074 research outputs found
Multi-orbital cluster perturbation theory for transition metal oxides
No full textWe present an extension of cluster perturbation theory to include many-body correlations associated with local e-e repulsion in real materials. We show that this approach can describe the physics of complex correlated materials where different atomic species and different orbitals coexist. The prototypical case of MnO is considered
Non-local exchange and correlation in surface calculation: an application to GaAs(110)
No full textThe self-consistent pseudopotential method has been applied to the determination of the electronic structure of the GaAs(110) surface in the framework of the Kohn-Sham density-functional theory, using the nonlocal exchange-correlation energy functional of Gunnarsson and Jones. It is shown that the inclusion of nonlocality in the description of the exchange-correlation energy does not change surface-state energies significantly. The behavior of the charge density and of the potential outside the surface and some measurable properties related to them, such as the corrugation parameters, is calculated and discussed
Quasiparticle band structure
No full textMany body effects influence the energy-versus-momentum relation that is measured in angle resolved photoemission experiments and the quasiparticle band structure may be significantly different from what is deduced within the independent particle model. In the case of cobalt many body effects are even more drastic than an energy renormalization giving rise to a quenching of quasiparticle peaks. Augmenting ab-initio band structure with many-body e-e
interactions we have obtained spin- and k-dependent self-energies, hole spectral functions and quasiparticle energies to be compared with photoemission spectra; our results show that e-e correlations are responsible for strong spin-dependent energy renormalizations
Progress in computational physics of matter: methods, software and applications
No full textThe understanding of the microscopic processes occurring in solids and liquids is a significant challange in computational physics. The rapid growth of computer power including the new paralell architectures has stimulated a ferment of new theoretical and computational ideas
Aspects of self-consistent procedures in surface pseudopotential calculations
No full textThe authors present a discussion of the main features of self-consistency for clean and chemisorbed surfaces in the local density functional formalism. The technical details of the procedure are analysed together with the behaviour of the various contributions to the surface potential. They show that the iterative approach to self-consistency can be made efficient and quick when the starting potential is properly chosen and the components of the potential more sensitive to the self-consistent process are singled out
Reentrant metallicity in the Hubbard model: the case of honeycomb nanoribbons
No full textBased on the cluster perturbation solution of the Hubbard Hamiltonian for a 2D honeycomb lattice, we present quasi-particle band structures of nanoribbons at half filling as a function of on-site electron-electron (e-e) repulsion. We show that, at moderate values of e-e interaction, ribbons with armchair-shaped edges exhibit an unexpected semimetallic behavior, recovering the original insulating character only at larger values of U
THEORETICAL INVESTIGATION OF THE FERMI LEVEL PINNING AT THE SB-GAAS(110) INTERFACE
No full textWe present the results of theoretical calculation of the electronic structure of the Sb-GaAs(110) interface in the submonolayer coverages perormed in the semiempirical TB scheme. Iterface states arising from the incomplete bonding of Sb atoms to the substarte apepar in the band gap; such states can be prsent also at higher coverages when some disorder exists, evidentiating a general mechanism for fermi lev pinning at the interfac
Three-Body Scattering Theory of Correlated Hole and Electron States
No full textWe describe a theoretical scheme for the determination of quasiparticle spectra starting from the energy band structure of a metal and treating the on-site Hubbard repulsion beyond the mean-field theory. The method relies upon an expansion of the many-body states in terms of uncorrelated states with a different number of electron-hole pairs. By truncating the expansion to include configurations with one or two pairs one can achieve approximate expressions of the electron and hole self-energies. The interparticle scattering matrices appearing in such expressions are conveniently calculated using the Faddeev approach. Calculations performed for a constant density of states allow us to illustrate the role of three-body correlations in the metal-insulator transitions
ELECTRON-STATES AT Zn(0001) SURFACE
No full textThe electronic structure of the Zn(0001) surface is analyzed through a realistic slab calculation with an accurate tight-binding sp-d model hamiltonian. The results are compared with a recent photoemission investigation of this surface. The comparison with noble and near-noble metal surfaces, with reference to the surface states in the s-p gap at the centre of the surface Brillouin zone, is also discussed
On-site correlation in valence and core states of ferromagnetic nickel
No full textWe present a method which allows us to include narrow-band correlation effects in the description of both valence and core states and we apply it to the prototypical case of nickel. The results of an ab initio band calculation are used as input mean-field eigenstates for the calculation of self-energy corrections and spectral functions according to a three-body scattering solution of a multiorbital Hubbard Hamiltonian. The calculated quasiparticle spectra show a remarkable agreement with photoemission data in terms of bandwidth, exchange splitting, satellite energy position of valence states, and spin polarization of both the main line and the satellite of the 3p core level
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