Erik Ingemar Tellgren

Forsker - Hylleraas-senteret
Bilde av Erik Ingemar Tellgren
English version of this page
Rom V218
Brukernavn
Besøksadresse Sem Sælands vei 26 0371 OSLO
Postadresse Postboks 1033 0315 OSLO

I am a researcher at CTCC. I have contributed to two quantum chemistry packages (DALTON and DIRAC), and am the main author of a third program (LONDON). LONDON was written from scratch and is a unique quantum-chemical tool to explore the effect of magnetic fields on molecules. Recently, I was awarded a research grant from the Norwegian Research Council to study molecular spin frustration due to relativistic effects and non-uniform magnetic fields.

My other research interests include:

  • Molecules in strong magnetic fields: Quantum chemical work has almost exclusively focused on weak magnetic fields, the effect of which can be modelled as slight perturbations to molecules. By directly modelling the magnetic field effects without recourse to perturbation theory, my research has resulted in novel computational techniques with different strengths and weaknesses. A strength is the ability to explore the exotic physics and chemistry of molecules subject to magnetic field strengths several stronger than what can be produced in a laboratory.
  • Development of Current-Density Functional Theory (CDFT): The most well-known form of Density Functional Theory is only valid in the absence of external magnetic fields. When magnetic vector potentials are placed on an equal footing with scalar potentials, one should also place the current density on an equal footing with the density. The resulting framework, CDFT, is much less developed in terms of practical approximations than DFT, and it remains an interesting challenge to incorporate current-dependence in practical functionals.
  • Formal aspects of DFT/CDFT: My research has helped understand some mathematical aspects of CDFT, such as the extension of Lieb's formulation of DFT to CDFT, the characterization of the class of current densities that can arise from valid quantum mechanical states (a version of the N-representability problem), the status of the Hohenberg-Kohn-like results in CDFT, etc.
  • Linear-scaling methods and PBC: Techniques for reducing the computational cost of SCF calculations on large systems as well as Periodic Boundary Conditions formulated using localized basis functions were among my first research projects. These themes have been not been the primary focus of recent research, but remain among my long-term interests.
Emneord: Kjemi, Teoretisk kjemi

Publikasjoner

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  • Tellgren, Erik & Helgaker, Trygve (2020). Strong Magnetic Field-Induced Chemical Bonding.
  • Penz, Markus; Laestadius, Andre; Tellgren, Erik; Ruggenthaler, Michael & Lammert, Paul (2020). Erratum: Guaranteed Convergence of a Regularized Kohn-Sham Iteration in Finite Dimensions. Physical Review Letters. ISSN 0031-9007. 125(24). doi: 10.1103/PhysRevLett.125.249902
  • Laestadius, Andre; Penz, Markus; Tellgren, Erik; Ruggenthaler, Michael; Kvaal, Simen & Helgaker, Trygve (2019). Guaranteed convergence of a regularized Kohn-Sham iteration in finite dimensions.
  • Tellgren, Erik; Helgaker, Trygve & Sen, Sangita (2019). Unifying kinetic energy density and current density in density-functional theory.
  • Tellgren, Erik; Helgaker, Trygve & Sen, Sangita (2019). Unifying kinetic energy density and current density in density-functional theory.
  • Tellgren, Erik; Helgaker, Trygve & Sen, Sangita (2019). Unifying kinetic energy density and current density in density-functional theory.
  • Fliegl, Heike; Helgaker, Trygve & Tellgren, Erik (2018). The effect of strong magnetic fields on the ring currents of tetraoxaisophlorin.
  • Tellgren, Erik (2018). Magnetic fields, convexity and gauge invariance in density functional theory.
  • Tellgren, Erik (2018). The Hohenberg-Kohn theorem in a Maxwell-Schrödinger setting.
  • Tellgren, Erik; Lange, Kai Kaarvann; Sagvolden, Espen; Kvaal, Simen; Austad, Jon & Reimann, Sarah [Vis alle 9 forfattere av denne artikkelen] (2018). Quantum chemistry for strong magnetic fields.
  • Sen, Sangita & Tellgren, Erik (2018). A local tensor that unifies kinetic energy density and vorticity dependent exchange-correlation functionals .
  • Sen, Sangita & Tellgren, Erik (2018). A local tensor that unifies kinetic energy density and vorticity dependent functionals in DFT.
  • Sen, Sangita & Tellgren, Erik (2018). Molecules in Strong Magnetic Fields.
  • Sen, Sangita & Tellgren, Erik (2018). Excited Molecules in Strong Magnetic Fields.
  • Helgaker, Trygve; Borgoo, Alex; Gauss, Jurgen; Hampe, Florian; Klopper, Wim & Reimann, Sarah [Vis alle 9 forfattere av denne artikkelen] (2018). Closed-Shell Molecular Paramagnetism.
  • Helgaker, Trygve; Borgoo, Alex; Dimitrova, Maria; Gauss, Jurgen; Hampe, Florian & Holzer, Christof [Vis alle 13 forfattere av denne artikkelen] (2018). Diamagnetism and Paramagnetism in Atoms and Molecules.
  • Helgaker, Trygve; Borgoo, Alex; Gauss, Jurgen; Hampe, Florian; Klopper, Wim & Stopkowicz, Stella [Vis alle 8 forfattere av denne artikkelen] (2018). Closed-Shell Molecular Magnetism.
  • Helgaker, Trygve; Borgoo, Alex; Gauss, Jurgen; Hampe, Florian; Klopper, Wim & Reimann, Sarah [Vis alle 9 forfattere av denne artikkelen] (2018). Closed-Shell Molecular Paramagnetism.
  • Laestadius, Andre; Penz, Markus; Tellgren, Erik; Ruggenthaler, Michael; Kvaal, Simen & Helgaker, Trygve (2018). Generalized Kohn-Sham iteration on Banach Spaces.
  • Tellgren, Erik (2017). Magnetic fields, convexity and gauge invariance in density functional theory.
  • Sen, Sangita & Tellgren, Erik (2017). Excited Molecules in Strong Magnetic Fields.
  • Tellgren, Erik; Teale, Andrew Michael; Ekström, Ulf Egil; Kvaal, Simen; Sagvolden, Espen & Helgaker, Trygve (2015). Current density functional theory for molecular systems in strong magnetic fields.
  • Helgaker, Trygve; Borgoo, Alex; Ekström, Ulf Egil; Furness, James; Hoffmann, Mark & Kvaal, Simen [Vis alle 12 forfattere av denne artikkelen] (2014). Density-Functional Theory in Magnetic Fields.
  • Teale, Andrew Michael; Furness, James; Tellgren, Erik; Ekström, Ulf Egil & Helgaker, Trygve (2014). Density Functional Theory for Molecules in Magnetic Fields.
  • Helgaker, Trygve; Hoffmann, Mark; Lange, Kai Kaarvann; Soncini, Alessandro & Tellgren, Erik (2014). Molecules in Strong Magnetic Fields.
  • Sagvolden, Espen; Tellgren, Erik; Ekström, Ulf Egil & Helgaker, Trygve (2014). Cusp based DFT functionals.
  • Sagvolden, Espen; Tellgren, Erik; Kvaal, Simen; Ekström, Ulf Egil; Teale, Andrew Michael & Helgaker, Trygve (2013). Building blocks of Current Density Functional Theory.
  • Sagvolden, Espen; Tellgren, Erik; Kvaal, Simen; Ekström, Ulf Egil; Teale, Andrew Michael & Helgaker, Trygve (2013). Building blocks of Current Density Functional Theory.
  • Kvaal, Simen; Ekström, Ulf Egil; Tellgren, Erik; Borgoo, Alex; Helgaker, Trygve & Sagvolden, Espen (2013). Moreau-Yosida regularization of DFT.
  • Ekström, Ulf Egil; Kvaal, Simen; Borgoo, Alex; Helgaker, Trygve; Sagvolden, Espen & Tellgren, Erik (2013). Moreau-Yosida regularization of DFT.
  • Helgaker, Trygve; Kaarvann, Lange Kai & Tellgren, Erik (2011). Molecules in strong magnetic fields. META. ISSN 1890-1956. s. 16–18.
  • Tellgren, Erik (2006). Desity-Fitting for the Coulomb interaction in periodic systems.
  • Tellgren, Erik (2006). Implementation of Periodic Boundary Conditions in DALTON.
  • Tellgren, Erik (2006). Implementation of Periodic Boundary Conditions in DALTON.
  • Tellgren, Erik & Helgaker, Trygve (2006). Introducing periodic boundary conditions into a molecular code.
  • Tellgren, Erik & Helgaker, Trygve (2006). Introducing periodic boundary conditions into a molecular code.
  • Austad, Jon; Helgaker, Trygve & Tellgren, Erik (2020). Theoretical Investigations of Molecular Electronic Structure in a Magnetic Field. Faculty of Mathematics and Natural Sciences, University of Oslo. ISSN 1501-7710. 2020(2295). Fulltekst i vitenarkiv
  • Trøyflat, Jostein; Helgaker, Trygve; Tellgren, Erik & Reine, Simen Sommerfelt (2015). Efficient methods for self-consistent field calculation of molecules in finite magnetic fields. Universitetet i Oslo.
  • Tellgren, Erik; Helgaker, Trygve; Ruud, Kenneth & Soncini, Alessandro (2009). Quantum-chemical method development for extended and magnetic systems. Universitetet i Oslo.

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Publisert 9. nov. 2010 14:25 - Sist endret 29. sep. 2020 14:52