NERSC Initiative for Scientific Exploration (NISE) 2011 Awards

Material Simulations in Joint Center for Artificial Photosynthesis (JCAP)

Nathan Lewis, California Institute of Technology

NISE project jcap

JCAP is a DOE funded energy hub at the $24M/year funding level. The goal is to develop systems which absorb lights and generate chemical fuels (e.g., water splitting, or convert CO2 to methonal). Material science research is at the heart of JCAP activities. More specifically, there are the following areas of researches: (1) Light absorber: finding the appropriate light absorber with the sufficient light absorbing ability and output enough potential for water splitting; (2) Catalysis: find the cheap and efficient alternative to the H- reduction and OH+ oxidation catalysts; (4) Membranes: find the membranes or other related designs which can separate the H2 and O2 gases, while permits the transport of proton; (5) Linker: find the molecule or solid state linkers, which lead the electron and hole from the light absorber to their respective catalysts. In all the above areas, theoretical calculations play an important role. They help to guide the experiment, narrow down the scope of experimentally to be tested materials, help to understand the processes and design the new catalysts.

In JCAP, we have about 7 theoretical groups (PIs) who are involved in doing material science simulations. Most of their simulations use large scale computations. These might include: DFT calculations for thousand atom systems for their atomic structures; GW calculation for 50 atom systems for their band gaps and band alignments; transport calculations for the electronic transport in the linker molecules; classical and ab initio molecular dynamics simulations for the catalytic processes; high order quantum mechanical calculations for the catalytic middle steps; and possibly massive atomic structure search either fornew crystal compounds, interface structure, and molecule/surface attachments. All these might need large computer resources. Each of the theoretical group might have a few postdocs. working in the JCAP project. Thus in total, we can have 20-30 users. Most of the groups have current NERSC accounts. But they are dedicated to other researches, not for JCAP activities. It is essential for us to have a dedicated account for JCAP calculations. On the other hand, all these calculations can be related to their original research in the original ERCAP account in terms of the techniques they are using. They are an extension to the JCAP scientific activity.

More specifically, we plan to carry out the following calculations: (1) Interface atomic structure between two semiconductor or semiconductor and metal. This is important especially for amorphous interface where the interface atomic structure is not well known, and this atomic structure affects the electronic structure of the interface; (2) Doping of the oxides. We plan to use the Z-scheme for light absorbing. In the Z-scheme, there are two light absorbing materials. One of them is oxide. But the band gap of a typical oxide is too large. We plan to dope the oxide to reduce the band gap. We will thus calculate different doping site and formation energy, and their related electronic structures; (3) Electron and hole transports across the linker molecules. We will study the transport mechanism and help to design newer molecules for better connection; (4) Catalysis. There are multiple steps to study the catalysis process. It might involve high level quantum mechanical calculations, and ab initio molecular dynamics simulations (MD). It might be a combination of the classical and ab initio MD simulations; (5) Membrane. We can simulate the membrane and its mixing with the nanowires or rods using classical MD simulations, especially to study the proton transport. For example, one can study whether a proton can pass through a graphene sheet, or graphene with 5-7 ring defects; (6) Electrode (or semiconductor) liquid interface. One important thing is to study how the electron might transfer from the electrode to the liquid molecule (e.g., water) which induces the electrochemical interaction. This might involve a time-domain style simulation where the electron follows the time-dependent Schrodinger’s equation.

While the main purpose for the JCAP work is to find the materials and systems which work as artificial photosynthesis, during the work, in order to carry out some of the simulations, we will also develop some methods (e.g., methods for large scale material simulation, to study the catalysis process, and for time domain simulation). We will also develop methods taking the advantageous of the architecture of the NERSC machine.