Seminar usually takes place on Thursday at 9:15 in lecture room of prof. Kvasnica 10th floor in Trója, V Holešovičkách 2, Praha 8
Future seminars:
Past seminars:
October 17, 2024
Calculation of bound states of positron with molecules.
Dr. Jaroslav Hofierka
Heidelberg
Maybe with inclusion of some discussion of ICD and ETMD.
October 24, 2024
Vibronic spectra at non-zero temperatures from coherence thermofield dynamics
Jiří Vaníček
École Polytechnique Fédérale de Lausanne
I will present several methods for evaluating vibrationally resolved electronic spectra at nonzero temperatures based on the coherence thermofield dynamics [1], which converts the “hard”, nonzero-temperature problem to an “easy” zero-temperature problem. We first transform the von Neumann evolution of the coherence component of the density matrix to the Schrödinger evolution of a “thermal” wavefunction in an augmented space with twice as many degrees of freedom. In the exact quantum approach [2], the thermal wavepacket is then propagated by solving the standard, zero-temperature Schrödinger equation with the split-operator Fourier method. To apply the method to realistic molecules, we combine it [1] with the on-the-
fly ab initio extended thawed Gaussian approximation, which accounts exactly for mode distortion, Duschinsky rotation, and Herzberg-Teller effects and partially for anharmonicity. Compared to the zero-temperature case, the finite-temperature calculation requires no additional ab initio electronic structure calculations. We apply the extended Gaussian thermofield dynamics to evaluate the symmetry-forbidden absorption spectrum of benzene, where all of the aforementioned effects contribute [1]. Finally, I will show an extension to two-dimensional vibronic spectroscopy [3].
REFERENCES: [1] J. Chem. Phys. 153, 024105 (2020), [2] J. Chem. Phys. 160, 084103 (2024), [3] J. Phys. Chem. Lett. 12, 2997 (2021).
October 31, 2024
Selected topics from summer conferences.
Martin Čížek, Zdeněk Mašín
ITF, MFF UK
We will discuss selected topics from the "4th DEA Club Meeting" (Potsdam), from worshop "Advances in theory of electronic resonances" (Telluride Colorado), LPHYS (Laser physics, Brasil), CESTC (Central European Sympozium on Theoretical Chemistry, Croatia), ICECream (ICEC, Germany).
November 7, 2024
Modelling of attosecond photoionization time-delays in atomic iodine and iodomethane.
Martin Crhán
ITF, MFF UK
During the last two decades the measurement of a new observable within pho-
toelectron spectroscopy has been unlocked. This observable is the (typicaly
attosecond) photoionization time-delay - the difference between the propaga-
tion time of the photoelectron and of a free particle with the same asymptotic
energy.
Our goal is to understand photoionization time-delays in attosecond streak-
ing of iodoalkanes at high photon energies around 100 eV, which probe the
iodine 4d shell. In collaboration with the experimental group of R. Kien-
berger of TU Munich our ultimate aim is to understand streaking from such
molecules deposited on surfaces. As a first step we focus on the study of an
isolated iodine atom and the CH3I molecule in the laboratory and molecular
frames. The main aim beeing to accurately describe the effect of the iodine
“giant dipole resonance” on time-delays in both atomic and molecular
environments.
To do this, we use the UKRmol+ suite which is able to calculate
a number of photoionization observables ranging from cross sections and
angular distribution parameters to 1-photon Wigner and 2-photon RABITT
delays. We utilize the newly implemented functionality of UKRmol+ to use
“effective core potentials” which naturally include scalar relativistic effects
and compare the results with all-electron calculations. Our models are able
to clearly separate the collective effects from the mean-field effects which
require detailed modeling of electron correlation and channel couplings.
Studying high energy photoelectrons is well suited for the development
of approximations. In the future we seek to use the accurate results and
experience from these two simple species to obtain a simplified, yet accurate
description of the photoionization through the use of, for instance, effective
molecular potentials. This effective description of streaking could then be
used to study the more complex iodoalkanes and to obtain a simple physical
picture of the process, where possible.
November 14, 2024
Photoelectron quantum state spectroscopy
David Busto
Lund University
Photoelectron spectroscopy, pioneered by Kai Siegbhan, is a powerful tool to study the structure of matter. This method relies on measuring the classical momentum of the photoelectrons emitted from a target following the absorption of a high energy photon. When ultrashort extreme ultraviolet pulses are used to ionize the target, the photoelectrons are characterized by a broad distribution of continuum states, forming, in the time domain, short electron wave packets. A key question is a whether this distribution is fully coherent, or if instead it only partially coherent, consisting of a statistical mixture states. Addressing this question requires a tomographic meausurement of the photoelectron density matrix.
In this seminar I will present a new photoelectron quantum state tomography scheme, KRAKEN, that we recently implemented experimentally. I will discuss the results obtained in helium and argon atoms, showing that the photoelectrons emitted from helium are pure, while in argon, owing the ion-photoelectron entanglement, the photoelectrons are a statistical mixture. These results show the quantum state of photoelectrons depends on the properties of the parent atom, opening new avenues for spectroscopy.
December 5, 2024
Domain Truncation, Absorbing Boundary Conditions, Schur Complements, and Padé Approximation.
Michal Outrata
Department of numerical mathematics, MFF UK.
In 1655, an Oxford professor John Wallis published his book Artihmetica Infinitorum -- The Arithmetic of Infinitesimals -- introducing the term continued fraction, which has later been used as the tool of choice in approximation theory for nearly 300 years, until the notation now bearing the name of Henri Padé became the one commonly used in the field. Around the time when Padé introduced his work -- namely in 1870 -- Hermann Schwarz introduced an iterative process for solving the Laplace problem, nowadays called the alternating Schwarz method. It was introduced as a theoretical tool but has since evolved into a broad family of associated methods -- the Schwarz methods. One of the important aspect of these methods is choosing the interface conditions through which the method propagates the subdomain solution information and one common class of these interface conditions is called absorbing boundary conditions (ABCs).
In this talk we marry these two areas -- continued fractions and ABCs -- and show for a model problem that the truncation of an unbounded domain by an artificial Dirichlet boundary condition placed far away from the domain of interest is equivalent to a specific absorbing boundary condition at the boundary of the domain of interest. We prove that the absorbing boundary condition thus obtained is a spectral Padé approximation about infinity of the transparent boundary condition. We also propose two additional ABCs motivated by this result and numerically show their efficiency for our test problem.