Research Areas & Themes

205 Furnas

The group at work: Jun, Sai, Zach, and Mojtaba in our lab space in 205 Furnas Hall

Coordination and Catalysis as Grand Challenges for Computational Chemistry

Coordination chemistry and catalysis pose some of the most formidable problems for electronic structure theory, molecular modeling, and simulations, but they also promise great rewards due to their fundamental and ubiquitous importance in fields as diverse as biology, medicine, chemical engineering, and materials science. The challenges and opportunities are extraordinary and we have hence made them the centerpiece of our research program.

The chemistry and physics of coordination compounds – in particular of transition metal complexes with partially filled d- or f-shells – is typically more involved than those of other compound classes. They are subject to a subtle interplay between core and ligand features, and a delicate balance of competing energy contributions (e.g., exchange, relativistic, dispersion, solvent, protein environment, and thermodynamic). This often leads to manifolds of low-lying, near-degenerate states of a sometimes radically varying nature. All this in turn gives rise to a wealth of unusual electronic, magnetic, and response phenomena. Prominent examples are temperature-dependent spin-crossovers, non-innocent ligand behavior and redox activity, Jahn-Teller distortions, bond-stretch isomerisms, conical intersections, and non-Born-Oppenheimer effects.

In catalysis the situation is further complicated since chemical transformations (i.e., bond-breaking/-formation as well as charge and energy transport processes) have to be considered on top of the already difficult coordination problem. The bulk phase structure and dynamics can play an important role, and the transition from homogenous to heterogeneous catalysis adds the issue of extended length scales. In biocatalysis we also have to account for macromolecular environments and their functional support of the catalytic mode of action. There are many potential reaction paths which have to be resolved for a mechanistic understanding, and the corresponding rate equations are very sensitive to small energy differences along the reaction coordinate. Both the thermodynamic as well as the kinetic aspects of a catalytic setup must be illuminated in order to establish insights into its activity and selectivity.

Following the advent of user-friendly, black-box program packages and abundant computing time, the number of computer-aided investigations in chemistry has grown substantially in recent years. The quality of the results and their interpretation is unfortunately too often unsatisfactory, though. Modern computational chemistry codes allow non-expert users to produce data but there are hardly any safeguards as to its validity or meaningfulness. Coordination chemistry and catalysis, however, are rich in traps and pitfalls in which stock calculations can fail.There are two basic lessons that are emphasized by these failures:

  1. Any computational tool has to be employed with particular care – the black-box idea of standard quantum chemistry does not apply to complicated problems. The real art of computational chemistry lies in the myriad of choices and decisions which largely determine the success and value of a study.
  2. Some problems are simply outside the reach of certain methods, even when they are utilized cautiously. If a method does not contain the physics required to capture the essence of a problem, it is bound to fail on it. The right choice of method for a given problem is critically important.

Our application oriented research recognizes these lessons: the difficulties of the tasks at hand are reflected in our carefully designed and executed investigations. Our method development work targets weaknesses which are prevalent in current numerical techniques. Our work is also concerned with the problem that the traditional protocols of computational chemistry reach their limit in comprehensive searches for new compounds, reactions, or materials, considering the vast chemical possibilities. We are thus pioneers of a paradigm that emphasizes an automated, high-throughput approach to computational chemistry. It allows for a systematic exploration of chemical spaces and provides a data foundation for the rational understanding of structure-property relationships.

State-of-the-Art Application of Computational Chemistry to Catalysis and Coordination Compounds

Our applied work focuses currently on the design of catalysts for photo(electro)chemical water splitting, the biocatalytic activation of small molecules, and new pathways in organocatalysis. It includes modeling efforts (i.e., the theoretical characterization) for given compounds and reactions, as well as the design and prediction (i.e., the theoretical engineering) of new ones. A special emphasis is given to the computation of observables (in particular spectroscopic data) to allow for an empirical verification of our findings and claims. In addition to employing conventional methods, we believe that some of the latest, cutting-edge techniques of computational chemistry deserve particular consideration for these applications. Such high-quality, high-profile studies could encourage a more dynamic adaptation of new methods by the community.

It is worth noting that there is an array of other interesting topics in coordination chemistry and catalysis which are also great subjects for computer-aided studies. Prime examples are molecular magnets and spintronics, batteries and energy storage materials, metal-organic frameworks, light-emitting diode complexes, dye-sensitized and hybrid photovoltaics, anti-cancer drugs, and intelligent contrast agents. If the opportunity for a suitable experimental collaboration emerge on one of these topics we would be happy to broaden our research portfolio accordingly.

Research Philosophy

We believe that the most interesting and relevant questions for theoreticians tend to develop from close collaborations with experimentalists. At the same time, experimental work generally benefits from (and often demands) the specialized expertise of theoreticians, e.g., to make guiding predictions or to provide a solid foundation for new discoveries. Experiments are usually time- and resource-intensive, so that support from theory can significantly boost productivity. Theory can also provide unique insights beyond the scope of empirical observation. There is thus every reason for both theoreticians and experimentalists to pursue a joint and comprehensive approach to progress in the chemical sciences.

Our research program combines both an application and a method development section, and it fosters symbiotic ties with experimentalists. Our goal is to learn from our experimentalist partners and identify worthwhile problems as they emerge, perform meaningful, state-of-the-art calculations on these problems, and utilize the gained experience as an inspiration for new methodological developments. Bringing together all these components in a discovery pipeline balances the individual need for specialization with the overarching imperative of interdisciplinarity. Truly challenging applications in computational chemistry require a substantive understanding of the available tools, in particular with regard to their weaknesses and limits of applicability. The latest additions to its methodological arsenal on the other hand are only useful if they are ultimately employed to real-world problems. We believe that an inclusive group design is ideal to accommodate students with different talents and interests, and to share crucial skills and expertise.