Gas adsorption in nanoporous materials such as zeolites and Metal-Organic Frameworks (MOFs) is a promising technology that can serve many purposes in modern-day society. Relevant applications that will be used in the near future are carbon capture and sequestration (to reduce CO₂ emissions from power plants) and hydrogen storage (for batteries in hydrogen-powered vehicles). This of course demands that new materials with specific properties are synthesized, for example carbon capture and sequestration requires that the nanoporous material shows selective adsorption for the guest molecules CO₂, N₂ and H₂O.

Computational simulations can be a valuable tool to discover novel candidate nanoporous materials that satisfy the criteria mentioned above, hereby seriously speeding up the otherwise very laborious experimental synthesis of a lot of materials. There are however a few remaining problems before reliable large-scale predictions can be inferred from the simulations. Unfortunately, accurate quantum-mechanical methods such as Coupled-Cluster (CC) or double-hybrid Density Functional Theory (DFT) are computationally too expensive to study the adsorption of guest molecules. One is forced to use classical potentials (or force fields (FF)) to efficiently sample guest insertions using e.g. Grand Canonical Monte Carlo (GCMC). Classical potentials are however either based on experiment (which is useless to investigate hypothetical materials) or extracted from high-level ab initio calculations (which requires a lot of work and thus can not be applied to a large database of materials). It is clear that further research is required that enables construction force fields that accurately describe gas adsorption in nanoporous materials with minimal effort.

Goal

The goal of this thesis is to come up with a procedure to derive force fields from ab initio reference data that accurately describe gas adsorption in nanoporous materials. This should be done in a way that both requires little human intervention (i.e. an automated procedure) and as little as possible ab initio input (i.e. a computationally tractable procedure).

As mainly non-covalent interactions govern the adsorption of guest molecules, we will focus on this part of the force field and work with rigid frameworks. Much progress has been made at the Center for Molecular Modeling regarding non-covalent force fields and a first model, that has been shown to reproduce experimental second virial coefficients, is available. This model will serve as a starting point for this master thesis. However, the model requires further testing and refinement for the intended systems of this proposal. One of the most interesting properties of the basic model, is that only three universal parameters need to be determined. This possibly allows to adapt the model to specific chemical compositions using a very limited amount of ab initio reference data. The student will need to perform and understand very accurate ab initio calculations (e.g. Coupled-Cluster), investigate methodologies to obtain accurate values for the universal parameters and finally assess the usefulness of the developed procedure for experimental researchers.

Mobility
This research topic will be conducted in the framework of a strong international network and if possible the student will be actively involved in work discussions with collaborative partners.

Motivation Appl. Phys.
Multiple aspects of molecular modeling will be important in this thesis, ranging from theoretical development (extending the non-bonded model) to implementation (python programming), computational work (evaluating the existing non-bonding model) and physical interpretation (interpretation of the results in practical applications).