• Were your results as expected, or did your research take other directions than outlined in your project description?

The main purpose of the CAS year was to explore chemistry in extreme magnetic fields and under high pressure. Before our stay at CAS, nothing was known about the stability of larger molecules containing elements beyond hydrogen and helium. During the year, we established that chemical molecules such as methane CH4 are indeed stable in magnetic fields such as those observed on magnetic white dwarfs. Moreover, a general pattern can now be discerned. Each covalent bond (with two paired electrons) -- such as the CH bond -- transforms itself into a paramagnetic bond (with two unpaired electrons) of the same type that we had previously discovered in H2. This is an exciting result, suggesting that molecules other than H2 and He2 exist and can be detected in the atmospheres of white dwarfs and, more generally, that chemistry in extreme magnetic fields is richer than previously speculated. 

On the other hand, we have not yet been successful in predicting a vibronic spectrum for H2 in strong magnetic fields, as needed for its experimental detection on magnetic white dwarfs. The difficulty is the correct matching of electronic states as the molecules rotates relative to the magnetic field vector. Such matching can in principle be done by hand, but the large number of states makes this unmanageable. We are instead using machine learning in an attempt to solve this problem.

An important goal of the CAS project was to elucidate the connections between high pressure and extreme magnetic fields, bearing in mind that both squeeze matter. We have performed an advanced study of atoms and molecules in a confinement potential and established how high-angular momentum states are stabilised by con-finement in precisely the same manner as by a strong magnetic field. Moreover, we have performed the first theoretical study of melting in strong magnetic fields. In agreement with the already established stabilisation of molecules in a magnetic field, we have found that the melting temperature of rare gases increases significantly in a strong magnetic field.

We are particularly proud of this study, since it combines a number of techniques for melting simulations and advanced electronic-structure calculations using density-functional theory and high-level coupled-cluster theory. This study would have been impossible to carry out without the collective expertise at CAS and their unique tools. Bearing in mind the combined high pressure and strong magnetic fields on white dwarf stars, this study may have experimental relevance.

We made considerable progress in the description of atomic and molecular electronic excitations and ionisation processes. Using coupled-cluster theory, we have very successfully studied the electronic structure of small closed-shell paramagnetic molecules, explaining their paramagnetism in an elegant manner in terms of three-level avoided crossings. We have moreover developed and applied several electronic-structure methods to study atomic and molecular excitation and ionization processes in a magnetic field. These studies have improved our understanding of the increased stability of atoms and molecules in strong magnetic further.

We have also successfully studied and developed DFT in magnetic fields, having established the usefulness of meta functionals for DFT in strong fields. This work was only possible since we had the best expertise in both DFT and coupled-cluster theory present in the CAS group.

During the CAS year, we made no progress in the study of quantum dots in magnetic fields. However, during our final conference at CAS, 'Atoms, molecules, and materials in extreme environments,' we made contact with a material scientist who pointed us in the right direction and to the right literature. We have since discovered many similarities between the behaviour of molecules in extreme environments and the behaviour of and coupled quantum dots ('artificial molecules') in laboratory-strength fields, forming an intriguing starting point for future research.

• How did your group work together during the year at CAS? 

During the CAS year, our group worked together in different ways. Several projects involved many of the members, who worked together in complementary ways. These projects greatly benefitted from the very extensive combined expertise of the group. At the same time, most if not all members also carried out research not directly related to the CAS project. This was a natural and expected manner of operation, bearing in mind that all the participants run research groups, which must be attended to on a regular basis.

• Why was a year at CAS important for this project?

Personally, I view the CAS year as very important for the study of chemistry in extreme environments -- in particular, strong magnetic fields. Thanks to CAS, I was able to invite to Oslo a number of excellent scientists with complementary skills and interest for an extended time and greatly advance this particular field of study. Many of the results and advances would have been impossible to achieve without a close collaboration over several months. Several of the participants had not previously concerned themselves with chemistry in extreme environments -- their participation has not only advanced the field as such but also extended the interest in this area of chemistry to influential research groups.

• Are there any plans for continuing the collaborations initiated during your stay at CAS?

I also view the CAS project as a fantastic starting point for further collaborations. The research and collaboration initiated at CAS are ongoing with planned visits to complete the work. In particular, we are aiming for a meeting of all group members in the second half of 2020 to finalise the projects begun at CAS.