We propose an unexplored class of absorbing materials for high-efficiency solar cells: heterostructures of transition-metal oxides. In particular, LaVO(3) grown on SrTiO(3) has a direct band gap ∼1.1 eV in the optimal range as well as an internal potential gradient, which can greatly help to separate the photogenerated electron-hole pairs. Furthermore, oxide heterostructures afford the flexibility to combine LaVO(3) with other materials such as LaFeO(3) in order to achieve even higher efficiencies with band-gap graded solar cells. We use density-functional theory to demonstrate these features.
Supercells are often used in ab initio calculations to model compound alloys, surfaces and defects. One of the main challenges of supercell electronic structure calculations is to recover the Bloch character of electronic eigenstates perturbed by disorder. Here we apply the spectral weight approach to unfolding the electronic structure of group III-V and II-VI semiconductor solid solutions. The illustrative examples include: formation of donor-like states in dilute Ga(PN) and associated enhancement of its optical activity, direct observation of the valence band anticrossing in dilute GaAs:Bi, and a topological band crossover in ternary (HgCd)Te alloy accompanied by emergence of high-mobility Kane fermions. The analysis facilitates interpretation of optical and transport characteristics of alloys that are otherwise ambiguous in traditional first-principles supercell calculations.
We study the effects of charge self-consistency within the combination of density functional theory (DFT; WIEN2K) with dynamical mean field theory (DMFT; W2DYNAMICS) in a basis of maximally localized Wannier orbitals. Using the example of two cuprates, we demonstrate that even if there is only a single Wannier orbital with fixed filling, a noteworthy charge redistribution can occur. This effect stems from a reoccupation of the Wannier orbital in k-space when going from the single, metallic DFT band to the split, insulating Hubbard bands of DMFT. We analyze another charge self-consistency effect beyond moving charge from one site to another: the correlation-enhanced orbital polarization in a freestanding layer of SrVO 3 .
In this paper we investigate the two manganese pnictides BaMn$_2$As$_2$ and
LaMnAsO, using fully charge self-consistent density functional plus dynamical
mean-field theory calculations. These systems have a nominally half-filled d
shell, and as a consequence, electronic correlations are strong, placing these
compounds at the verge of a metal-insulator transition. Although their crystal
structure is composed of similar building blocks, our analysis shows that the
two materials exhibit a very different effective dimensionality, LaMnAsO being
a quasi-two-dimensional material in contrast to the much more three-dimensional
BaMn$_2$As$_2$. We demonstrate that the experimentally observed differences in
the N\'eel temperature, the band gap, and the optical properties of the
manganese compounds under consideration can be traced back to exactly this
effective dimensionality. Our calculations show excellent agreement with
measured optical spectra.Comment: 9 pages, 9 figure
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