17 research outputs found
Linear and Second-order Optical Response from First Principles
We present a full formalism for the calculation of the linear and
second-order optical response for semiconductors and insulators. The
expressions for the optical susceptibilities are derived within perturbation
theory. As a starting point a brief background of the single and many particle
Hamiltonians and operators is provided. As an example we report calculations of
the linear and nonlinear optical properties of the mono-layer InP/GaP (110)
superlattice. The features in the linear optical spectra are identified to be
coming from various band combinations. The main features in the second-order
optical spectra are analyzed in terms of resonances of peaks in linear optical
spectra. With the help of the strain corrected effective-medium-model the
interface selectivity of the second-order optical properties is highlighted.Comment: 10 pages 4 figures, conference & physica script
All-electron Exact Exchange Treatment of Semiconductors: Effect of Core-valence Interaction on Band-gap and -band Position
Exact exchange (EXX) Kohn-Sham calculations within an all-electron
full-potential method are performed on a range of semiconductors and insulators
(Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps
are not as close to experiment as those obtained from previous pseudopotential
EXX calculations. Full-potential band-gaps are also not significantly better
for semiconductors than for insulators, as had been found for
pseudopotentials. The locations of -band states, determined using the
full-potential EXX method, are in excellent agreement with experiment,
irrespective of whether these states are core, semi-core or valence. We
conclude that the inclusion of the core-valence interaction is necessary for
accurate determination of EXX Kohn-Sham band structures, indicating a possible
deficiency in pseudopotential calculations.Comment: 4 pages 2 fig
Optical Response of Solid CO as a Tool for the Determination of the High Pressure Phase
We report first-principles calculations of the frequency dependent linear and
second-order optical properties of the two probable extended-solid phases of
CO--V, i.e. and . Compared to the parent
phase the linear optical susceptibility of both phases is much smaller. We find
that and differ substantially in their linear optical
response in the higher energy regime. The nonlinear optical responses of the
two possible crystal structures differ by roughly a factor of five. Since the
differences in the nonlinear optical spectra are pronounced in the low energy
regime, i.e. below the band gap of diamond, measurements with the sample inside
the diamond anvil cell are feasible. We therefore suggest optical experiments
in comparison with our calculated data as a tool for the unambiguous
identification of the high pressure phase of CO.Comment: 4 pages 2 fig
Lithiation of InSb and CuSb : A Theoretical Investigation
In this work the mechanism of Li insertion/intercalation in the anode
materials InSb and CuSb is investigated by means of the first principles
total energy calculations. The total charge densities for the lithiated
products of the two compounds are presented. Based on these results the change
in the bonding character on lithiation is discussed. Further, the isomer shift
for InSb and CuSb and there various lithiated products is reported. The
average insertion/intercalation voltage and volume expansion for transitions
from InSb to LiInSb and CuSb to LiCuSb are calculated and found to
be in good agreement with the experimental values. These findings help to
resolve the controversy regarding the lithiation mechanism in InSb.Comment: 5 pages 3 figure
First-principles approach to noncollinear magnetism: Towards spin dynamics
A description of noncollinear magnetism in the framework of spin-density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived within the optimized effective potential (OEP) framework. With the example of a magnetically frustrated Cr
monolayer it is shown that the resulting magnetization density exhibits much more noncollinear structure than standard calculations. Furthermore, a time-dependent generalization of the noncollinear OEP method is well suited for an ab initio description of spin dynamics. We also show that the magnetic moments of solids Fe, Co, and Ni are well reproduced
Linear and Second-order Optical Response of the III-V Mono-layer Superlattices
We report the first fully self-consistent calculations of the nonlinear
optical properties of superlattices. The materials investigated are mono-layer
superlattices with GaP grown on the the top of InP, AlP and GaAs (110)
substrates. We use the full-potential linearized augmented plane wave method
within the generalized gradient approximation to obtain the frequency dependent
dielectric tensor and the second-harmonic-generation susceptibility. The effect
of lattice relaxations on the linear optical properties are studied. Our
calculations show that the major anisotropy in the optical properties is the
result of strain in GaP. This anisotropy is maximum for the superlattice with
maximum lattice mismatch between the constituent materials. In order to
differentiate the superlattice features from the bulk-like transitions an
improvement over the existing effective medium model is proposed. The
superlattice features are found to be more pronounced for the second-order than
the linear optical response indicating the need for full supercell calculations
in determining the correct second-order response.Comment: 9 pages, 4 figures, submitted to Phy. Rev.
Optical second harmonic generation in Yttrium Aluminum Borate single crystals (theoretical simulation and experiment)
Experimental measurements of the second order susceptibilities for the second
harmonic generation are reported for YAl3(BO3)4 (YAB) single crystals for the
two principal tensor components xyz and yyy. First principles calculation of
the linear and nonlinear optical susceptibilities for Yttrium Aluminum Borate
YAl3(BO3)4 (YAB) crystal have been carried out within a framework of the
full-potential linear augmented plane wave (FP-LAPW) method. Our calculations
show a large anisotropy of the linear and nonlinear optical susceptibilities.
The observed dependences of the second order susceptibilities for the static
frequency limit and for the frequency may be a consequence of different
contribution of electron-phonon interactions. The imaginary parts of the second
order SHG susceptibility chi_{123}^{(2)}(omega), chi_{112}^{(2)}(omega),
chi_{222}^{(2)}(omega), and chi_{213}^{(2)}(omega) are evaluated. We find that
the 2(omega) inter-band and intra-band contributions to the real and imaginary
parts of chi_{ijk}^{(2)}\l(omega) show opposite signs. The calculated second
order susceptibilities are in reasonably good agreement with the experimental
measurements.Comment: 16 pages, 11 figure
Response theory for time-resolved second-harmonic generation and two-photon photoemission
A unified response theory for the time-resolved nonlinear light generation
and two-photon photoemission (2PPE) from metal surfaces is presented. The
theory allows to describe the dependence of the nonlinear optical response and
the photoelectron yield, respectively, on the time dependence of the exciting
light field. Quantum-mechanical interference effects affect the results
significantly. Contributions to 2PPE due to the optical nonlinearity of the
surface region are derived and shown to be relevant close to a plasmon
resonance. The interplay between pulse shape, relaxation times of excited
electrons, and band structure is analyzed directly in the time domain. While
our theory works for arbitrary pulse shapes, we mainly focus on the case of two
pulses of the same mean frequency. Difficulties in extracting relaxation rates
from pump-probe experiments are discussed, for example due to the effect of
detuning of intermediate states on the interference. The theory also allows to
determine the range of validity of the optical Bloch equations and of
semiclassical rate equations, respectively. Finally, we discuss how collective
plasma excitations affect the nonlinear optical response and 2PPE.Comment: 27 pages, including 11 figures, version as publishe