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This is a benchmark study, for valence excitation energies in the multilevel coupled cluster (MLCC) framework. The information resulting from lower level of theory is used to generate correlated natural transition orbitals (CNTOs) for the high level calculations by including the information from both the singles and the doubles excitation vectors. The CNTOs are included in the active space according to certain thresholds corresponding to the eigenvalues of the orbitals. The MLCC results for valence excitation energies in the inactive space are calculated using coupled cluster singles and doubles (CCSD), and the active space are calculated using CCSD with perturbative triples (CC3). The errors relative to full CC3 depends on the thresholds. In general to obtain errors less than 10% on needs to include approximately 60-70% of the orbital space for the investigated molecules.

Aalborg University applies a problem-based learning model. Each semester all students form groups. Group members formulate and agree upon a problem they want to address, within their course of study, and write a long report on their findings (length depends on the year of study, the number of group members etc.). Key principles for the choice problem is praxis-orientation, interdisciplinarity, and contextualisation. To facilitate inter-disciplinarity two supervisors – a disciplinary and a contextual – might be associated with student groups. A team of seven undergraduate students of Chemistry, Environmental technology and Biotechnology study-programme at Aalborg University, and thei contextual superviso worked on the problem “What is the risk of methane migration into houses situated on the terminated landfill “Skrænten” in Hjørring, Denmark?” The work consisted of both a technical part and a contextual part. In the technical part we investigated the theoretical foundation of methane production in landfills and we measured the concentration of methane at different places at the landfill Skrænten in Hjørring. In the contextual part a NUSAP analysis was done on the risk assessment of the gas-producing landfill that had been carried out by the local authorities.