Molecular Electronic-Structure Theory

The primary focus in the Janus Juul Eriksen Group falls within the development of novel theories for decomposing complex electronic-structure theory. We continuously look to explore how the concept of spatial locality may be used to unravel intriguing chemical phenomena. As a means for achieving this and to probe and simulate the inner workings of molecular and solid-state systems, we involve a wealth of interesting aspects of modern-day quantum chemistry as well as contemporary machine-learning techniques.

Research

Our current activities span much of the spectrum of electronic-structure theory, all the way from developing methods with the capabilities to simulate modest-sized systems at near-exact accuracy to developing widely applicable methods operating at a much more limited level of accuracy.

The need for calibration and advancements on leading approximations to formally exact theory is highly relevant; possibly more so today than throughout the past two or three decades. This is particularly with the advent of novel forms of computation in mind. In our research activities, we keep this central. Simultaneously, we work under the belief that simulations which lend themselves to established methods in quantum chemistry can benefit from being viewed through more localized and alternative perspectives. This shift has the potential to refine and advance our understanding of how best to approximate the electron correlation problem.

Finally, we break down molecular simulations into contributions from individual atoms or functional groups which allows for a more precise resolution of the training data. This can significantly improve the accuracy of machine-learning models in chemistry, which is an area we are increasingly interested in contributing to.

Join the Lab

In my lab, I am actively striving to attract and develop a heterogeneous group of talented people through scientific excellence, attentive teaching, as well as careful and supporting mentoring, all with an appreciation of diversity, equality, and inclusion at its core

DTU students interested in joining the group for BSc and MSc research projects can contact me at any time.

Funded PhD and postdoc positions will be advertised here and on career.dtu.dk whenever available. However, qualified applicants are always welcome to contact me at any time to discuss possible projects and opportunities to apply for funding. There are many fellowship schemes available through which you might be able to secure funding. If your profile is strong and your interests match ours, we will enthusiastically support bids


Rescent research topics

Lossless property decompositions of HF & KS-DFT into either bond-wise or atomic contributions.

I've introduced a new and robust decompositions of mean-field Hartree-Fock (HF) and Kohn-Sham density functional theory (KS-DFT) relying on the use of localized molecular orbitals and physically sound charge population protocols, cf. ref 1. The new lossless property decompositions, which allow for partitioning 1-electron reduced density matrices into either bond-wise or atomic contributions, are intended to be employed in possible applications as an interpretative tool in the rationalization of certain electronic phenomena as well as for exposing and amplifying compositional features in the context of machine-learned quantum chemistry. Recent applications of the theory include ref. 2.

The DECODENSE code is open source: https://github.com/januseriksen/decodense
Comparison of bond- and atom-partitioned contributions (in units of Hartree) to the total KS-DFT (TPSSh xc functional) energy of the benzene molecule (Fig. from doi/10.1063/5.0030764).
Assessments of modern near-exact electronic structure theory.

Leading a broad, international consortium of research groups, I've worked on the blind assessment of a wide range of contemporary near-exact electronic structure methods. Specifically, we've reported (in ref. 3) on the findings of a blind challengedevoted to determining the frozen-core, full configuration interaction (FCI) ground-state energy of the benzene moleculein a standard correlation-consistent basis set of double-ζ quality. Subsequently, I've been invited to comment on the status of current state-of-the-art approaches in a perspective on the field (ref. 4), nearly a century on from the dawn of modern quantum mechanics.

Other research topics

  • Many-Body Expanded Full Configuration Interaction
    Near-exact properties for both weakly and strongly correlated molecular systems in extended basis sets.

  • HPC- and GPU-Accelerated Quantum Chemistry
    Efficient implementation of coupled cluster methods on parallel CPU and GPU hardware.

  • Coupled Cluster Perturbation Theory
    Theoretical development of Lagrangian-based many-body perturbation theory.

  • Local Coupled Cluster Methods
    Implementation and application of the DEC-CCSD(T) computational method.

  • Polarizable Embedding Theory
    Polarizable solvent modelling by means of either DFT or many-body methods.

Group members