About me

Vebjørn is currently a part of the ERC project REGAL at OsloMet , where he has been a PhD Research Fellow under the supervision of Associate Professor Andre Laestadius since the autumn of 2023.

Vebjørn is happy to announce the 2026 workshop on the Foundations and Extensions of Density-Functional Theory to be held in Oslo from the 20th to the 24th of April 2026. Please see the webpage for further details.

Vebjørn is together with Vegard organising a seminar series for the Mathematical Modelling Group, the OsloMet Quantum Hub, and the REGAL Project. An update schedule can be found her. If you are interested in presenting and/or attending the seminar series, please do not hesitate to contact Vebjørn.
Vebjørn also co-hosted a workshop on the Foundations and Extensions of Density-Functional Theory in Oslo from the 2nd to the 6th of December 2024. Link to webpage.

Research Interests

Vebjørn is currently a PhD candidate working on the mathematical aspects of quantum chemistry, in particular that of density-functional theory (DFT). These aspects include the Moreau-Yosida regularisation, extensions of DFT such as quantum electrodynamics density-functional theory (QEDFT), and exact constraints in DFT.

At the moment he and the group are working on applying and analysing methods from DFT to quantum electrodynamics (QED). In particular, the study of the quantum Rabi model and the generalised Dicke model using the Lieb approach to DFT which has lead to two publications (Articles II. and III.). In addition to allowing for the analytical study of a QEDFT, these models serves as an example in which the methods of DFT can be explored by paper and pen. As such, these models allow us to illustrate several technical aspects of DFT that is inaccessible analytical means in the standard DFT and can thus help to understand several intricate mathematical details of the theory. Future works aim to further understand the ground-state properties of these models and develop rigorous functional approximations in these simplified QED settings.

He is also working on Kohn-Sham inversion for periodic systems by use of the Moreau-Yosida regularisation of DFT. The analysis of Kohn-Sham inversion includes devising an algorithm for the inversion procedure as well as strict error bounds on the inverted potential. This mathematical inversion scheme has in a recent publication (Article I. below) been demonstrated to accurately recover the elusive exhchange-correlation potential for three representative bulk materials. In particular, the inversion scheme has been successfully applied to the semiconductors silicon (Si) and gallium arsenide (GaAs), as well as an ionic salt, namely potassium chloride (KCl). Future work aim to address questions regarding convergence properties, both of the proximal point and in the regularisation parameter, further develop the error bounds, and apply the inversion procedure to densities obtained from other high quality sources such as full configuration-interaction calculations or experiments.

Publications

1. Kohn-Sham inversion with mathematical guarantees (Phys. Rev. B 111, 205143, 2025)
   
2. Quantum-Electrodynamical Density-Functional Theory Exemplified by the Quantum Rabi Model, J. Phys. Chem. A 2025, 129, 9, 2337–2360
   
3. Density-Functional Theory for the Dicke Hamiltonian, J. Stat. Phys. 192, 61, 2025
   

Teaching

No current teaching responsibilities.

Previously, during the two years as a master’s student at the University of Oslo, Vebjørn was a teaching assistant in the courses FYS2160 – Thermodynamics and Statistical Physics, FYS-MEK1110 – Mechanics, and FYS1100 – Mechanics and Modelling (twice).

Links

• Master’s thesis in DUO Research Archive.
• Presentation on a QEDFT model at the Center for Advanced Study at the Norwegian Academy of Science and Letters, February 2024
• Poster on Kohn-Sham inversion at the Mathematical and Numerical Analysis of Electronic Structure Models (MANUEL) conference in Stuttgart, Germany, September 2024
• Presentation at the autumn meeting of the Quantum Chemistry and Modeling section of the Norwegian Chemical Society, Trondheim, November 2024
• Presentation at Workshop on Foundations and Extensions of DFT, at OsloMet, December 2024
• Poster on DFT exemplified by the quantum Rabi model presented at the Center for Advanced Study at the Norwegian Academy of Sciences and Letters, Oslo, March 2025
• Seminar at the Hylleraas Centre for Quantum Molecular Sciences at the University of Oslo, April 2025
• Poster at the WATOC conference in Oslo, June 2025
• Poster at the MWM 2025 summer school in Pisa, September 2025
• Presentation at the autumn meeting of the Quantum Chemistry and Modeling section of the Norwegian Chemical Society, Tromsø, October 2025