Research

A. Multi-scale model of electrified solid-liquid interface

Broadly speaking, multiscale modeling refers to the art of representing different regions of a complex system with different levels of theory, depending on the problem at hand, to simulate longer timescale and / or larger lengthscales than which is possible with the most accurate description. In order to study electrochemical reactions at solid-liquid interface under constant applied bias, the electrode surface and the substrate needs to be treated quantum mechanically. In several such reactions, solvent usually plays a passive role without actively participating in the reaction. Thus, a QM description of the solvent may be superfluous. Hence, a multi-scale model is desirable where the electrode surface and the subtrate are described with a first principle based method, e.g. DFT, while atomistic description of the solvent is replaced by a statistical description like RISM. The objective of this project is to implement 3D-RISM within the framework of AIMD (Figure 1) in CP2K software package.

Figure 1: Schematic representation of the proposed coarse grained model for a Au|water|Ne simulation cell. In this set-up, Ne is employed to charge the Au electrode

B. QM/MM/MD study of catalytic reactions in solution

QM/MM molecular dynamics is a powerful tool to study catalytic reactions in aqueous solutions where the intricate H-bonding networks of water molecules play an important role, e.g. reactions involving long-range proton transfer processes. Here, at least a few water molecules, along with the catalyst, need to be included within the QM region while the rest of the water molecules can be treated classically with force field parameters. Recently, we studied the mechanism of O 2 reduction by a mononuclear Cu-electrocatalyst. Experimental studies suggest that the reaction proceeds via a binuclear metal complex. Complementary computational studies revealed the details of the electronic structure of the metal centers and the disposition of the ligand framework during the catalytic cycle. Interestingly, we found two thermodynamically viable pathways (Figure 2) for the critical O-O bond cleavage reaction, both involving long-range proton transfer processes that can be mediated by solvent (water) molecules. The objective of this project is to study these two pathways using QM/MM/MD methodology.

Figure 2: Schematic representation of the computed catalytic cycle for O 2 reduction.