The aim of our research is to invent techniques that will enable us to elucidate the electronic structure of transition metal containing materials with partially filled d/f orbitals in the presence of strong non-adiabaticity and environmental fluctuations. Our work attempts to provide a molecular level understanding of phenomena that are of critical importance in heterogeneous catalysis, multiferroics for electronics, superconductivity and are even relevant in biology for bird navigation via magnetoreceptors and enzyme catalyzed redox reaction of small molecules.
To develop such methods we make use of three powerful paradigms from electronic structure theory:
- Tensor decomposition/contraction, which has already given us density matrix renormalization group and low/linear scaling methods.
- Quantum Monte Carlo, which has seen a significant revival due to the development of methods that work in the space of gaussian basis sets such as full configuration interaction quantum Monte Carlo and auxiliary field quantum Monte Carlo.
- Quantum embedding theories, which are indispensable for describing inherently macroscopic processes such as symmetry breaking, collective excitation, and phase transitions.
The combination of these techniques can enable us to treat all the elements in the periodic table (not just organic chemistry) routinely; allow the quantum simulation of large proteins and engineering of new quantum materials from first principles. Although these methods will be broadly applicable, the systems of immediate interest are metalloenzymes and transition metal oxides.
Transition metal containing clusters are central to life because they are the active sites of proteins catalyzing reactions such as, nitrogen reduction, hydrolysis of water, cleavage of C-H bonds, reduction of CO2 to carbohydrates etc. These reactions are not only necessary for life but are also of great importance in the chemistry of sustainable energy. These clusters have been the topic of intensive research for decades and a wide range of molecular spectroscopies ranging from Mössbauer, EPR/ENDOR, XAS, MCD have been used. Theoretical techniques have a uniquely important role to play in this research by helping us infer the underlying electronic structure based on the spectroscopic measurements. Further, theory can help to bridge the gap in reaction pathways by providing clues to the structure of short-lived intermediates that are very hard to detect experimentally. Theoretical understanding of these enzymes will help us design biomimetic catalysts using cheap earth abundant transition metals.
Transition metal oxides
Transition metal oxides are finding applications in industrial processes related to energy conversion and storage like batteries, water splitting photocatalysis, oxygen evolution/reduction reactions etc. Their electronic properties show unusually high sensitivity to their structure and thus can be fine-tuned for improving catalytic efficiency and selectivity. But unfortunately, this process is often carried out by an expensive ad hoc trial and error method. A more systematic catalyst design would be possible if one could reliably calculate properties such as band gaps, density of states, adsorption energies etc. But traditional methods are very unreliable for such systems, for example, different density functionals give widely varying band gaps for transition metal oxides, such as NiO. Rigorous, first principle electronic structure methods have a crucial role to play in guiding catalyst design by screening a whole range of materials to short list a few promising candidates.