Dyson orbitals with OpenMolcas

OpenMolcas, a free open-source project branched off the Molcas program package, has now the possibility to calculate Dyson orbitals and photoionization cross-sections in the sudden approximation limit. This means that the capabilities which have been available within our external code written by Gilbert Grell are now inherent to the OpenMolcas. You are welcome to try it!

The details of the implementation can be found in the OpenMolcas article:

I. Fernández Galván, M. Vacher, A. Alavi, C. Angeli, F. Aquilante, J. Autschbach, J.J. Bao,   S.I. Bokarev, N.A. Bogdanov, R.K. Carlson, L.F. Chibotaru, J. Creutzberg, N. Dattani, M.G. Delcey, S.S. Dong, A. Dreuw, L. Freitag, L. M. Frutos, L. Gagliardi, F. Gendron, A. Giussani, L. González, G. Grell, M. Guo, C.E. Hoyer, M. Johansson, S. Keller, S. Knecht, G. Kovačević, E. Källman, G. Li Manni, M. Lundberg, Y. Ma, S. Mai, J.P. Malhado, P.-Å. Malmqvist, P. Marquetand, S.A. Mewes, J. Norell, M. Olivucci, M. Oppel, Q.M. Phung, K. Pierloot, F. Plasser, M. Reiher, A.M. Sand, I. Schapiro, P. Sharma, C.J. Stein, L.K. Sørensen, D.G. Truhlar, M. Ugandi, L. Ungur, A. Valentini, S. Vancoillie, V. Veryazov, O. Weser, T.A. Wesołowski, P.-O. Widmark, S. Wouters, A. Zech, J.P. Zobel, and R. Lindh, OpenMolcas: From Source Code to Insight, J. Chem. Theory Comput. 15, 5925 (2019).


In the center of the graphical abstract, you can see the L-edge photoelectron spectrum of the Fe(II) aqueous ion – our guinea pig for testing different protocols.

Thanks to Joel Creuzberg and Jesper Norell for implementation and Per-Åke Malmqvist for programming support!

Workshop ‘Molecular quantum dynamics beyond bound states‘

This year from September 2nd to 4th I organize a workshop

Molecular quantum dynamics beyond bound states’

which will be held in Rostock and is sponsored by the DFG.


This focused workshop will address theoretical methods to describe various aspects of ionization and autoionization spectroscopy, the interaction of molecules and atoms with intense laser fields, and subsequent electronic and non-adiabatic dynamics.

There will be no conference fee. Everybody is cordially invited to take part. Please register by sending me an email.

Habilitation accomplished!

On the 29th of January, I have successfully accomplished the final part of my Habilitation – the scientific talk on the general topic “Novel X-ray probes for the structure of matter.” In December, I have also done a lecture for physics students at the Bachelor level on the mathematical methods in physics, which constituted the second phase of Habilitation. The title of the thesis itself was “Spectroscopy and Photoinduced Dynamics of Transition Metal Complexes.”


People who have contributed to the scientific background of my Habilitation and who had at that moment still been affiliated with our group. Left to right: Andy Kaiser, Tobias Möhle, Gilbert Grell, Oliver Kühn, me, Olga Bokareva, Vladislav Kochetov. Others who contributed can be found under the “former members” on the People page.


I would like to thank all those people who have supported me on a way to this milestone, those who have encouraged me, provided advice, discussions with whom have driven my inspiration, and those who have done me invaluable favor making my ideas come true. I would like to express special thanks to my wife Dr. Olga Bokareva and my host Prof. Dr. Oliver Kühn. Of course, I am grateful to Prof. Dr. Leticia González and Prof. Dr. Peter Saalfrank for reviewing my thesis.

Benchmarking Auger code for neon atom

Auger effect is a manifestation of the correlated motion of electrons in atoms, molecules, and extended phases. In a nutshell, the Auger electron emission contains three steps: the creation of a relatively deep hole upon absorption of high-energy light,  the non-radiative refill of this hole by some outer valence electron, and the ionization of a system, where the energy of the second step is used to remove another outer valence electron. Despite its complexity, this process plays an essential role in X-ray spectroscopy and radiation damage. For low-Z elements, it is even dominating over the simple radiative decay (fluorescence).

We have recently extended our computational protocol for X-ray spectroscopy to allow for the calculation of Auger spectra. A first step – benchmarking of the results for a well-studied system – is published in Rhys. Rev. A.:

Gilbert Grell, Oliver Kühn, Sergey I. Bokarev Multireference quantum chemistry protocol for simulating autoionization spectra: Test of ionization continuum models for the neon atom Phys. Rev. A 100 (2019) 042512.


In this article, we address the whole array of different approximations which can be employed in the calculation of such an intricate observable as Auger decay rate. This array has multiple dimensions: level of quantum chemistry applied, choice of the ionic potential generating the outgoing wave function, treatment of non-orthogonality of the model outgoing wave to the bound electron functions, choice of the coupling operator, etc. With this, our study compares some popular and routinely used variants with low costs to more elaborate but also more accurate ones. Finally, the recommendations on the combination of different approximations are formulated.

Andy Kaiser defended his Master thesis

On the 3rd of December, Andy Kaiser has defended his Master thesis under the title “Theoretical Approach to Angular-Resolved Photoelectron Spectroscopy.” In his work, Andy elaborated on a theoretical approach to predict laser pump-photoelectron probe spectra with angular resolution. It enables a more detailed interpretation of the experimental spectra within our collaboration with Helmholtz Zentrum in Berlin, see, e.g., our joint publications [1], [2], and [3].

Andy will continue in our group as a Ph.D. student focussing on the theoretical aspects of X-ray spectroscopy as applied to molecular aggregates and exciton transfer properties.

STC 2019

From 22 to 26 September 2019, around 300 Scientists from 18 countries have met at the University of Rostock. The focus of the 13 invited lectures, 26 contributed talks and 200 poster presentations has been put on the spectroscopy and light-induced dynamics. The scope of the discussed applications started from the processes in the small molecules in the gas phase to the biological systems and extended photoactive materials. It was a great pleasure for us as organizers that this event has been devoted to the 600th anniversary of the University of Rostock.


Photo ITMZ Rostock.

A short report on this conference can be found in the article in Nachrichten aus der Chemie:

O. Kühn, S. Bokarev*, R. Ludwig In Rostock: 55. Symposium für Theoretische Chemie, Nachrichten aus der Chemie 68 (2020), 65.

I would like to thank all participants and the local organizing committee for helping to make this event happen.

Review on theoretical X-ray spectroscopy

A review of the theoretical developments to predict various kinds of soft X-ray spectra has been published by us recently. It describes how different observables can be extracted from the theoretical calculations: absorption (XAS), photoionization (PES or XPS), resonant inelastic scattering (RIXS), and Auger. The main focus is on L-edge spectra of transition metals and in particular on multi-reference methods as they appear to be essential for this type of systems. However, the review also contains a brief overview of other methods and applications. Enjoy!


Matsubara-like dynamics for vibronic spectroscopy

I forgot to write about a publication which appeared at the end of the last year. It is a logical continuation of the previous works of Sven Karsten on the semi-classical description of vibronic spectra. That is when both electronic and nuclear motion of a molecule is excited.


This time Sven has elaborated on the imaginary time-shifted  correlation functions and applied a Matsubara approximation to a ring polymer which is residing partly on the excited potential energy surface and partly on the ground state one, as has been described in previous publication. This approximation filters out high-frequency vibrations of the ring polymer, leaving only the low-frequency “smooth” distortions. The idea is that the high-frequency counterpart is anyway cut by the Boltzmann distribution at the finite temperature. However, strictly speaking, one cannot call this approximation just Matsubara as there is an abrupt change in the ring due to different potentials it is evolving according to. That is why we call it Matsubara-like.

I hope that this approach upon the proper generalization to more complicated molecules will be a step towards reliable simulation of vibrionic spectra with semi-classical methods.