Erik Ingemar Tellgren
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.