T>0 ensemble state density functional theory revisited

A logical foundation of equilibrium state density functional theory in a Kohn-Sham type formulation is presented on the basis of Mermin's treatment of the grand canonical state. it is simpler and more satisfactory compared to the usual derivation of ground state theory, and free of remaining open points of the latter. It may in particular be relevant with respect to cases of spontaneous symmetry breaking like non-collinear magnetism and orbital order.Comment: 7 pages, no figure

Varying Cu-Ti hybridization near the Fermi energy in Cux_{x}TiSe2_{2}: Results from supercell calculations

The properties of Cu$_{x}$TiSe$_{2}$ are studied by band structure calculation based on the density functional theory for supercells. The density-of-states (DOS) for $x$=0 has a sharply raising shoulder in the neighborhood of the Fermi energy, $E_F$, which can be favorable for spacial charge modulations. The Cu impurity adds electrons and brings the DOS shoulder below $E_F$. Hybridization makes the Ti-d DOS at $E_F$, the electron-phonon coupling and the Stoner factor very large. Strong pressure dependent properties are predicted from the calculations, since the DOS shoulder is pushed to higher energy at a reduced lattice constant. Effects of disorder are also expected to be important because of the rapidly varying DOS near $E_F$.Comment: 5 pages, 4 figures 2 table

Violation of non-interacting V\cal V-representability of the exact solutions of the Schr\"odinger equation for a two-electron quantum dot in a homogeneous magnetic field

We have shown by using the exact solutions for the two-electron system in a parabolic confinement and a homogeneous magnetic field [ M.Taut, J Phys.A{\bf 27}, 1045 (1994) ] that both exact densities (charge- and the paramagnetic current density) can be non-interacting $\cal V$-representable (NIVR) only in a few special cases, or equivalently, that an exact Kohn-Sham (KS) system does not always exist. All those states at non-zero $B$ can be NIVR, which are continuously connected to the singlet or triplet ground states at B=0. In more detail, for singlets (total orbital angular momentum $M_L$ is even) both densities can be NIVR if the vorticity of the exact solution vanishes. For $M_L=0$ this is trivially guaranteed because the paramagnetic current density vanishes. The vorticity based on the exact solutions for the higher $|M_L|$ does not vanish, in particular for small r. In the limit $r \to 0$ this can even be shown analytically. For triplets ($M_L$ is odd) and if we assume circular symmetry for the KS system (the same symmetry as the real system) then only the exact states with $|M_L|= 1$ can be NIVR with KS states having angular momenta $m_1=0$ and $|m_2|=1$. Without specification of the symmetry of the KS system the condition for NIVR is that the small-r-exponents of the KS states are 0 and 1.Comment: 18 pages, 4 figure

Crystal Symmetry, Electron-Phonon Coupling, and Superconducting Tendencies in Li2_2Pd3_3B and Li2_2Pt3_3B

After theoretical determination of the internal structural coordinates in Li$_2$Pd$_3$B, we calculate and analyze its electronic structure and obtain the frequencies of the two $A_g$ phonons (40.6 meV for nearly pure Li mode, 13.0 meV for the strongly mixed Pd-Li mode). Pd can be ascribed a $4d^{10}$ configuration, but strong 4d character remains up to the Fermi level. Small regions of flat bands occur at -70 meV at both the $\Gamma$ and X points. Comparison of the Fermi level density of states to the linear specific heat coefficient gives a dynamic mass enhancement of $\lambda$ = 0.75. Rough Fermi surface averages of the deformation potentials $D$ of individual Pd and Li displacements are obtained. While is small, ~ 1.15 eV/\AA is sizable, and a plausible case exists for its superconductivity at 8 K being driven primarily by coupling to Pd vibrations. The larger d bandwidth in Li$_2$Pt$_3$B leads to important differences in the bands near the Fermi surface. The effect on the band structure of spin-orbit coupling plus lack of inversion is striking, and is much larger in the Pt compound.Comment: 8 pages and 8embedded figures, to be appeared in PR

On the electronic structure of CaCuO2 and SrCuO2

Recent electronic structure calculations for the prototypical lowdimensional cuprate compounds CaCuO2 ans SrCuO2 performed by Wu et. al. (J. Phys.: Condens. Matter v. 11 p.4637 (1999))are critically reconsidered, applying high precision full-potential bandstructure methods. It is shown that the bandstructure calculations presented by the authors contain several important inconsistencies, which make their main conclusions highly questionable.Comment: 4 pages, 3 figures, submitted to J. Phys. Condens. Matte

Calculation of the static and dynamical correlation energy of pseudo-one-dimensional beryllium systems via a many-body expansion

Low-dimensional beryllium systems constitute interesting case studies for the test of correlation methods because of the importance of both static and dynamical correlation in the formation of the bond. Aiming to describe the whole dissociation curve of extended Be systems we chose to apply the method of increments (MoI) in its multireference (MR) formalism. However, in order to do so an insight into the wave function was necessary. Therefore we started by focusing on the description of small Be chains via standard quantum chemical methods and gave a brief analysis of the main characteristics of their wave functions. We then applied the MoI to larger beryllium systems, starting from the Be6 ring. First, the complete active space formalism (CAS-MoI) was employed and the results were used as reference for local MR calculations of the whole dissociation curve. Despite this approach is well established for the calculation of systems with limited multireference character, its application to the description of whole dissociation curves still requires further testing. After discussing the role of the basis set, the method was finally applied to larger rings and extrapolated to an infinite chain

Deriving the Hirshfeld partitioning using distance metrics

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