N. E. Christensen

Self-consistent electronic structures of MgO and SrO

Abstract The LMTO-method is used to calculate the band structure of the alkaline-earth oxides MgO and SrO. The cohesive energy and equilibrium lattice constant are also calculated. The results are compared with experiments and other theoretical calculations.

Fermi surface and effective masses for the heavy-electron superconductors UPt3

Local-density-approximation (LDA) calculations for the Fermi-surface extremal cross-sectional areas of UPt{sub 3} are presented and compared to deHaas-van Alphen experiments of Taillefer et al. The topology of the calculated surfaces is in excellent agreement with experiment and allows a determination of the directional dependence of the anisotropic mass-renormalization factor. The source of this renormalization is briefly discussed. 12 refs., 4 figs., 2 tabs.

Low-energy excitations in heavy fermion systems

Abstract Band structure effects play an important role in determining the low-energy excitations in heavy fermion systems. The influence of coherence is evidenced by the recent de Haas-van Alphen experiments where well-defined Fermi surfaces for the heavy quasiparticles are observed and determined. Quasiparticles states in highly correlated electron systems can be described within the renormalized band method which merges realistic ab initio band calculations with phenomenological Fermi liquid considerations. In the present paper we compare calculated Fermi surfaces and quasiparticle bands of heavy fermion compounds with measured dHvA data. Emphasis is placed on the question: how do high effective masses and crystalline electric field (CEF) splitting influence the Fermi surface topology? Under which conditions can one expect conventional band theory to predict the correct Fermi surface?

Thermoelectric properties of chalcopyrite type CuGaTe2 and chalcostibite CuSbS2

Electronic and transport properties of CuGaTe2, a hole-doped ternary copper based chalcopyrite type semiconductor, are studied using calculations within the Density Functional Theory and solving the Boltzmann transport equation within the constant relaxation time approximation. The electronic band structures are calculated by means of the full-potential linear augmented plane wave method, using the Tran-Blaha modified Becke-Johnson potential. The calculated band gap of 1.23 eV is in agreement with the experimental value of 1.2 eV. The carrier concentration- and temperature dependent thermoelectric properties of CuGaTe2 are derived, and a figure of merit of zT = 1.69 is obtained at 950 K for a hole concentration of 3.7·1019 cm−3, in agreement with a recent experimental finding of zT = 1.4, confirming that CuGaTe2 is a promising material for high temperature thermoelectric applications. The good thermoelectric performance of p-type CuGaTe2 is associated with anisotropic transport from a combination of heavy...

Electronic structure of CsAu

Abstract Self-consistent non-relativistic and relativistic LMTO band structure calculations have been carried out for CsAu. In the non-relativistic model CsAu is a metal, whereas — in agreement with experiments — the relativistic calculations predict CsAu to be a semiconductor. The gap is not caused by the spin-orbit coupling. The importance of the core-like Cs-5 s and Cs-5 p states for the alloy formation is discussed, and charge distribution calculations are used to illustrate the ionic nature of the bonding.

Band structure and heterojunctions of II–VI materials

Abstract Selfconsistent first principles calculations of the electronic structures of II–VI semiconductor compounds as well as of superlattices composed of alternating layers of II–VI compounds are presented. The importance of a proper treatment of the outermost d states and of relativistic effects is stressed. The superlattice calculations are used to derive valence-band offsets at interfaces and “absolute deformation potentials”. The offsets derived from the self-consistent supercell calculations are compared to those obtained from the self-consistent supercell calculations are compared to those obtained by means of model theories (‘dielectric mid-gap energy’ model). Lattice matched as well as strained-layer systems are considered.

Calculated deformation potentials in Si, Ge, and GeSi

Abstract We have calculated electronic deformation potentials of Si, Ge, and zinc-blende-like GeSi for both hydrostatic as well as uniaxial strain along the [001] direction. The calculations have been performed with the self-consistent relativistic linear muffin-tin orbital (LMTO) method, including spin-orbit coupling, and show that the uniaxial spin-dependent deformation potential b 2 = −(0.05 ± 0.05) eV for both Si, Ge, and GeSi. The volume scaling parameters of the spin-orbit splittings Δ 0 and Δ 1 , d lnΔ 0,1 / d ln V , were calculated to be ≈ −0.6 for all three materials investigated. The error in the E 0 gap introduced by the use of the local-density approximation is corrected by the introduction of extra potentials included self-consistently in the calculation, thus leading to pressure coefficients of the direct and indirect gaps which compare well with experiments and other recent calculations.

“Force theorem” and elastic constants of solids

Abstract The so-called “Force Theorem” derived by Andersen describes how the change in the total energy of an electron system can be calculated to first order in a virtual displacement. It is demonstrated here, how this theorem can be applied in calculation of elastic constants of crystals although this in fact requires calculation of total-energy changes accurate to second order in the distortion parameter.

Band offsets in tetrahedral semiconductors

Experimental and theoretical determinations of the valence band offsets at heterojunctions between tetragonal semiconductors are reviewed. The physical mechanisms underlying the offset are illustrated on the basis of midgap level theories, in particular the dielectric midgap energy version (DME). Results obtained with the DME method for several nearly lattice‐matched heterojunctions are presented and critically compared with experimental data and the results of other theoretical evaluations.

Deformation potentials of the direct gap of diamond

Abstract The deformation potentials corresponding to uniaxial, hydrostatic stress and Raman phonons are calculated with the LMTO-method for the Γ 25 , and Γ 15 states of the direct gap of diamond. They are compared with the results of other calculations and with available experimental data.