Alternative energy research can greatly benefit from ab initio simulation that provides molecular level insight into the nature of chemical bonds and excited states. The level of detail found using these methods is extremely high and not often attainable via other means. However, many first principles methods are too costly for routine use in realistic systems due to poor scaling with system size. To alleviate this problem, our research group develops and applies state-of-the-art first-principles methods and support tools for the description of molecular catalysts and solar energy conversion systems.
Discovering mechanisms of catalysis to guide experiments toward increased rates and selectivity. New methods are being developed in the group to navigate complex reaction pathways with minimal computational and human effort. These tools (one example is the Freezing String Method, see Selected Publications below) allow the study and discovery of catalytic processes even with limited a priori chemical insight. These methods are applied to difficult energy-related problems such as CO2 reduction and methane conversion. This approach identifies the strengths and limitations of existing catalysts at an atomistic level to aid in the design of improved catalytic systems.
Characterizing the fundamental behavior of excited states in light harvesting materials. Solar cells and photocatalysts may be tuned to substantially higher efficiency when the character and interactions among electronically excited states are known. This level of detail, however, is especially hard to obtain due to the high cost of existing electronic structure methods that can treat excited states. New methods (such as Restricted Active Space Spin Flip) allow investigation of single and multiple exciton states in realistic models of molecular light harvesters and photocatalysts. The mechanistic information gained from these studies will lead to the development of highly efficient solar materials such as those that employ singlet fission, where a single photon is converted into two electron-hole pairs.
1. P. M. Zimmerman, Z. Zhang, and C. B. Musgrave, "Singlet fission in pentacene through multi-exciton quantum states," Nature Chemistry, 2, 648 (2010).
2. P. M. Zimmerman, Z. Zhang, and C. B. Musgrave, "Simultaneous Two Hydrogen Transfer as an Effective Mechanism for Selective CO2 Reduction," Inorganic Chemistry, 49(19), 8724 (2010).
3. P. M. Zimmerman, F. Bell, D. Casanova, M. Head-Gordon, "Mechanism for singlet fission in tetracene and pentacene: from single exciton to two triplets," Journal of the American Chemical Society, 133, 19944-19952 (2011).
4. A. Behn, P. M. Zimmerman, A. T. Bell, M. Head-Gordon, "Efficient exploration of reaction paths via a freezing string method," Journal of Chemical Physics, 135, 224108 (2011).
5. A. Mlinar, P. M. Zimmerman, F. E. Celik, M. Head-Gordon, A. T. Bell, "Effects of Bronsted Acid Site Proximity on the Oligomerization of Propene in H-MFI," Journal of Catalysis, 288, 65 (2012).