| 1. |
- Eriksson, Olle, et al.
(författare)
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Many-body projector orbitals for electronic structure theory of strongly correlated electrons
- 2005
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Ingår i: INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY. - : Wiley. - 0020-7608 .- 1097-461X. ; 105:2, s. 160-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a technique to evaluate projector functions to be used, e.g., in self-interaction corrected versions of the Kohn-Sham equation (or in the LSDA+U method). The projector functions reproduce by construction the expectation values of spin and orbital moments (or any other property one is interested in) for the atomic many-body state. We therefore refer to these projector functions as many-body projector orbitals (MBPO). We describe how, once these projector states have been calculated, one can use them in any electronic structure method for a solid or molecule, to calculate ground-state properties of materials with strongly correlated states.
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| 2. |
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| 3. |
- Grechnev, Alexei, et al.
(författare)
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Balanced crystal orbital overlap population : a tool for analysing chemical bonds in solids
- 2003
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 15:45, s. 7751-7761
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Tidskriftsartikel (refereegranskat)abstract
- A new tool for analysing theoretically the chemical bonding in solids is proposed. A balanced crystal orbital overlap population (BCOOP) is an energy resolved quantity which is positive for bonding states and negative for antibonding states, hence enabling a distinction between bonding and antibonding contributions to the chemical bond. Unlike the conventional crystal orbital overlap population (COOP), BCOOP handles correctly the situation of crystal orbitals being nearly linear dependent, which is often the case in the solid state. Also, BCOOP is much less basis set dependent than COOP. A BCOOP implementation within the full-potential linear muffin tin orbital method is presented and illustrated for Si, TiC and Ru. Thus, BCOOP is compared to the COOP and crystal orbital Hamilton population (COHP) for systems with chemical bonds ranging from metallic to covalent character.
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| 4. |
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| 5. |
- Grechnev, Alexei, et al.
(författare)
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Layered compound Nb3SiC2 predicted from first-principles theory
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85:15, s. 3071-3073
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Tidskriftsartikel (refereegranskat)abstract
- A previously unobserved ternary carbide, Nb3SiC2, belonging to the family of the so-called Mn+1AXn or MAX phases is predicted from first-principles calculations. It has a theoretical bulk modulus of 296 Gpa, wich is much higher than that of Ti3SiC2. The new phase is metastable with a formation energy of +0.02 eV/atom. We suggest that the phase may possibly be synthesized using thin film technology. The chemical binding of Nb3SiC2 is investigated using the balanced crystal orbital overlap population indicator and it is found to be dominated by the formation of Nb4D-C 2p covalent bonds.
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| 6. |
- Grechnev, Alexei, et al.
(författare)
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Theory of bulk and surface quasiparticle spectra for Fe, Co, and Ni
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:3, s. 035107-
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Tidskriftsartikel (refereegranskat)abstract
- The correlated quasiparticle band structure of iron, cobalt, and nickel is investigated within the dynamical mean-field theory formalism using the recently developed full-potential linear-muffin-tin-orbital-based local-density approximation plus dynamical mean-field theory (LDA+DMFT) code. Detailed analysis of the calculated electron self-energy, density of states, and the spectral density is presented for these metals. It has been found that all these elements show strong correlation effects for majority-spin electrons, such as strong damping of quasiparticles and formation of a satellite state below the bottom of d bands. In particular, our work clearly predicts the existence of a photoemission satellite for bcc iron. The LDA+DMFT data for fcc nickel and cobalt (111) surfaces and bcc iron (001) surface are also presented. The electron self-energy is found to depend strongly on the number of nearest neighbors, and it practically reaches the bulk value already in the second layer from the surface. The dependence of correlation effects on the dimensionality of the problem is also discussed.
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| 7. |
- Grechnev, Alexei, et al.
(författare)
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Thermodynamics of a two-dimensional Heisenberg ferromagnet with dipolar interaction
- 2005
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 71:2, s. 024427-
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamics of quantum and classical two-dimensional (2D) Heisenberg models with long-range dipole-dipole interaction has been investigated using various forms of self-consistent spin-wave theory (SSWT). It has been found that SSWT gives a much lower transition temperature T-c than the free-magnon (spin-wave) theory. For the classical spin, the T-c from SSWT lies within 9% of the Monte Carlo value, making SSWT the best approximation among those considered. It is proven that the random phase approximation vertex corrections to SSWT are rather small. The results depend strongly on the value of the spin, emphasizing the importance of using the quantum and not the classical 2D Heisenberg model even for large spins such as S=7/2.
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| 8. |
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| 9. |
- Monachesi, P., et al.
(författare)
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Ab-initio calculation of depth resolved optical anisotropy of the Cu (110) surface
- 2003
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Ingår i: Physical Review B. ; 68, s. 35426-
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the surface dielectric anisotropy (SDA) and the reflectance anisotropy of the relaxed Cu-(110) surface using the ab initio self-consistent full potential linear-muffin-tin orbital method within the local-density approximation. Besides interpreting the spectra in terms of transitions involving surface and/or bulk states, we carry out a depth depending scanning of them, from surface to bulk, with the resolution of one atomic layer. We show that the SDA mainly arises in the vacuum region above the surface and in the first atomic layer.
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| 10. |
- Souvatzis, Petros, et al.
(författare)
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Elastic properties of Mg(1-x)AlxB2 from first principles theory
- 2004
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16:29, s. 5241-5250
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Tidskriftsartikel (refereegranskat)abstract
- Elastic properties of Mg(1−x)AlxB2 have been studied from first principles. The elastic constants (c11, c12, c13, c33 and c55) have been calculated, in the regime of x = 0 to 0.25. From these calculations the ratio between the bulk modulus and shear modulus (B/G) as well as the ratio between the two directional bulk moduli (Ba/Bc) have been evaluated. Our calculations show that the ratio Ba/Bc decreases monotonically as the aluminium content is increased, whereas the ratio B/G is well below the empirical ductility limit, 1.75, for all concentrations. In addition, we analyse the electronic structure and the nature of the chemical bonding, using the balanced crystal orbital overlap population (BCOOP) (Grechnev et al 2003 J. Phys.: Condens. Matter 15 7751) and the charge densities. Our analysis suggests that, while aluminium doping decreases the elastic anisotropy of MgB2 in the a and c directions, it will not change the brittle behaviour of the material considerably.
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