263 research outputs found
Distinctive character of electronic and vibrational coherences in disordered molecular aggregates
Coherent dynamics of coupled molecules are effectively characterized by the
two-dimensional (2D) electronic coherent spectroscopy. Depending on the
coupling between electronic and vibrational states, oscillating signals of
purely electronic, purely vibrational or mixed origin can be observed. Even in
the "mixed" molecular systems two types of coherent beats having either
electronic or vibrational character can be distinguished by analyzing
oscillation Fourier maps, constructed from time-resolved 2D spectra. The
amplitude of the beatings with the electronic character is heavily affected by
the energetic disorder and consequently electronic coherences are quickly
dephased. Beatings with the vibrational character depend weakly on the
disorder, assuring their long-time survival. We show that detailed modeling of
2D spectroscopy signals of molecular aggregates providesdirect information on
the origin of the coherent beatings.Comment: 7 pages, 4 figures, 1 tabl
Time-domain chirally-sensitive three-pulse coherent probes of vibrational excitons in proteins
The third order optical response of bosonic excitons is calculated using the
Green's function solution of the Nonlinear Exciton Equations (NEE) which
establish a quasiparticle-scattering mechanism for optical nonlinearities. Both
time ordered and non ordered forms of the response function which represent
time and frequency domain techniques, respectively, are derived. New components
of the response tensor are predicted for isotropic ensembles of periodic chiral
structures to first order in the optical wavevector. The nonlocal nonlinear
response function is calculated in momentum space, where the finite
exciton-exciton interaction length greatly reduces the computational effort.
Applications are made to coupled anharmonic vibrations in the amide I infrared
band of peptides. Chirally-sensitive and non sensitive signals for alpha
helices and antiparallel beta sheets are compared.Comment: 26 pages, 6 figure
Thermalization of open quantum systems using the multiple-Davydov-D2 variational approach
Numerical implementation of an explicit phonon bath requires a large number
of oscillator modes in order to maintain oscillators at the initial temperature
when modeling energy relaxation processes. An additional thermalization
algorithm may be useful in controlling the local temperature. In this paper we
extend our previously proposed thermalization algorithm [M. Jaku\v{c}ionis and
D. Abramavi\v{c}ius, Phys. Rev. A 103, 032202 (2021) ] to be used with the
numerically exact multiple-Davydov-D2 trial wave function for simulation of
relaxation dynamics and spectroscopic signals of open quantum systems using the
time-dependent Dirac-Frenkel variational principle. By applying it to the
molecular aggregate model, we demonstrate how the thermalization approach
significantly reduces the numerical cost of simulations by decreasing the
number of oscillators needed to explicitly simulate the aggregate's environment
fluctuations while maintaining correspondence to the exact population
relaxation dynamics. Additionally, we show how the thermalization can be used
to find the equilibrium state of the excited molecular aggregate, which is
necessary for simulation of the fluorescence and other spectroscopic signals.
The thermalization algorithm we present offers the possibility to investigate
larger system-bath models than was previously possible using the
multiple-Davydov-D2 trial wave function and local heating effects in molecular
complexes
Probing environment fluctuations by two-dimensional electronic spectroscopy of molecular systems at temperatures below 5 K
Citation: Rancova, O., Jankowiak, R., & Abramavicius, D. (2015). Probing environment fluctuations by two-dimensional electronic spectroscopy of molecular systems at temperatures below 5 K. Journal of Chemical Physics, 142(21), 18. doi:10.1063/1.4918584Two-dimensional (2D) electronic spectroscopy at cryogenic and room temperatures reveals excitation energy relaxation and transport, as well as vibrational dynamics, in molecular systems. These phenomena are related to the spectral densities of nuclear degrees of freedom, which are directly accessible by means of hole burning and fluorescence line narrowing approaches at low temperatures (few K). The 2D spectroscopy, in principle, should reveal more details about the fluctuating environment than the 1D approaches due to peak extension into extra dimension. By studying the spectral line shapes of a dimeric aggregate at low temperature, we demonstrate that 2D spectra have the potential to reveal the fluctuation spectral densities for different electronic states, the interstate correlation of static disorder and, finally, the time scales of spectral diffusion with high resolution. (C) 2015 AIP Publishing LLC
Many-body Green's function approach to attosecond nonlinear X-ray spectroscopy
Closed expressions are derived for resonant multidimensional X-ray
spectroscopy using the quasiparticle nonlinear exciton representation of
optical response. This formalism is applied to predict coherent four wave
mixing signals which probe single and two core-hole states. Nonlinear X-ray
signals are compactly expressed in terms of one- and two- particle Green's
functions which can be obtained from the solution of Hedin-like equations at
the level.Comment: 10 pages and 3 figures (To appear in Physical Review B
Sum-over-states vs quasiparticle pictures of coherent correlation spectroscopy of excitons in semiconductors; femtosecond analogues of multidimensional NMR
Two-dimensional correlation spectroscopy (2DCS) based on the nonlinear
optical response of excitons to sequences of ultrafast pulses, has the
potential to provide some unique insights into carrier dynamics in
semiconductors. The most prominent feature of 2DCS, cross peaks, can best be
understood using a sum-over-states picture involving the many-body eigenstates.
However, the optical response of semiconductors is usually calculated by
solving truncated equations of motion for dynamical variables, which result in
a quasiparticle picture. In this work we derive Green's function expressions
for the four wave mixing signals generated in various phase-matching directions
and use them to establish the connection between the two pictures. The formal
connection with Frenkel excitons (hard-core bosons) and vibrational excitons
(soft-core bosons) is pointed out.Comment: Accepted to Phys. Rev.
Advancing hierarchical equations of motion for efficient evaluation of coherent two-dimensional spectroscopy
To advance hierarchial equations of motion as a standard theory for quantum
dissipative dynamics, we put forward a mixed Heisenberg--Schrodinger scheme
with block-matrix implementation on efficient evaluation of nonlinear optical
response function. The new approach is also integrated with optimized
hierarchical theory and numerical filtering algorithm. Different configurations
of coherent two-dimensional spectroscopy of model excitonic dimer systems are
investigated, with focus on the effects of intermolecular transfer coupling and
bi-exciton interaction
Effects of tunable excitation in carotenoids explained by the vibrational energy relaxation approach
V. B. acknowledges funding by the Leverhulme Trust Research Project Grant RPG-2015-337. J. H. and C. N. L. acknowledge funding by the Austrian Science Fund (FWF): START project Y 631-N27. D. A. acknowledges support by the Research Council of Lithuania (No MIP-090/2015). G. C. acknowledges support by the European Research Council Advanced Grant STRATUS (ERC-2011-AdG No. 291198). G. C. and J. H. acknowledge funding by Laserlab-Europe (EU-H2020 654148)
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