212 research outputs found
Benchmark density functional theory calculations for nano-scale conductance
We present a set of benchmark calculations for the Kohn-Sham elastic
transmission function of five representative single-molecule junctions. The
transmission functions are calculated using two different density functional
theory (DFT) methods, namely an ultrasoft pseudopotential plane wave code in
combination with maximally localized Wannier functions, and the norm-conserving
pseudopotential code Siesta which applies an atomic orbital basis set. For all
systems we find that the Siesta transmission functions converge toward the
plane-wave result as the Siesta basis is enlarged. Overall, we find that an
atomic basis with double-zeta and polarization is sufficient (and in some cases
even necessary) to ensure quantitative agreement with the plane-wave
calculation. We observe a systematic down shift of the Siesta transmission
functions relative to the plane-wave results. The effect diminishes as the
atomic orbital basis is enlarged, however, the convergence can be rather slow.Comment: 10 pages, 7 figure
Band Gap Tuning and Defect Tolerance of Atomically Thin Two- Dimensional Organic-Inorganic Halide Perovskites
Organic–inorganic
halide perovskites have proven highly
successful for photovoltaics but suffer from low stability, which
deteriorates their performance over time. Recent experiments have
demonstrated that low dimensional phases of the hybrid perovskites
may exhibit improved stability. Here we report first-principles calculations
for isolated monolayers of the organometallic halide perovskites (C<sub>4</sub>H<sub>9</sub>NH<sub>3</sub>)<sub>2</sub>MX<sub>2</sub>Y<sub>2</sub>, where M = Pb, Ge, Sn and X,Y = Cl, Br, I. The band gaps
computed using the GLLB-SC functional are found to be in excellent
agreement with experimental photoluminescence data for the already
synthesized perovskites. Finally, we study the effect of different
defects on the band structure. We find that the most common defects
only introduce shallow or no states in the band gap, indicating that
these atomically thin 2D perovskites are likely to be defect tolerant
Anharmonic stabilization and band gap renormalization in the perovskite CsSnI<sub>3</sub>
Amongst the X(Sn,Pb)Y perovskites currently under scrutiny for their
photovoltaic applications, the cubic B- phase of CsSnI is arguably
the best characterized experimentally. Yet, according to the standard harmonic
theory of phonons, this deceptively simple phase should not exist at all due to
rotational instabilities of the SnI octahedra. Here, employing
self-consistent phonon theory we show that these soft modes are stabilized at
experimental conditions through anharmonic phonon-phonon interactions between
the Cs ions and their iodine cages. We further calculate the renormalization of
the electronic energies due to vibrations and find an unusual opening of the
band gap, estimated as 0.24 and 0.11 eV at 500 and 300 K, which we attribute to
the stretching of Sn-I bonds. Our work demonstrates the important role of
temperature in accurately describing these materials.Comment: 12 pages, 4 figure
Städtischen Lieferverkehr umweltgerecht gestalten
STĂ„DTISCHEN LIEFERVERKEHR UMWELTGERECHT GESTALTEN
Städtischen Lieferverkehr umweltgerecht gestalten / Sommer, Karsten (Rights reserved) ( -
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