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  • Overend recipients Samuel Stoneburner and Kajari Bera
    04/11/19

    Two outstanding students receive Overend Award in Physical Chemistry

Kajari Bera and Samuel Stoneburner

Kajari Bera and Samuel “Sam” Stoneburner have received the 2018-19 Overend Award in Physical Chemistry. This award honors outstanding physical chemistry graduate student researchers. Kajari, a fourth-year graduate student working with Professor Renee Frontiera, is the award winner in the experimental physical chemistry area. Sam, a fifth-year graduate student advised by Professor Laura Gagliardi, is the award winner in the theory/computation area. The Overend Award is named after Professor John Overend who was a physical chemist in the department from 1960 to 1984. The award was created in 1991 through the efforts of Professor Paul Barbara.

Kajari Bera

Kajari Bera

Kajari’s research is focused broadly on applications and advances in using the femtosecond stimulated Raman spectroscopy technique to examine solid-state materials. It involves determining how solar cells made out of organic molecules could be made more efficiently. Specifically, she is determining how different molecular vibrational motions, or the collective motion of the atoms within a molecule, can be used to create more efficient solar cells. She uses a combination of ultrafast spectroscopic techniques in conjunction with theoretical modeling to determine how and where energy flows in organic photovoltaics.

She is the first graduate student in Professor Frontiera's group to work on this type of project, and her contributions include growing and characterizing molecular crystals using physical vapor transport, building and maintaining an ultrafast Raman spectroscopic system, performing density functional theory calculations at the Minnesota Supercomputing Institute, and working with synthetic chemists to design molecules to test her hypotheses. Kajari has been focusing on the ultrafast dynamics of rubrene, a molecule known to undergo singlet fission, a process by which a single photoexcitation results in the collection of two electrons. In collaboration with Professor Christopher Douglas, he has written a first author paper on this work that was published last year in the Journal of Physical Chemistry Letters.

She also has submitted a first-author paper to the Journal of Physical Chemistry A that describes a significant technical advance to the ultrafast Raman data acquisition process. In this work, Kajari and her co-workers demonstrate a pulse shaping approach that minimizes background signal interference, which should enable facile data interpretation of complex solid-state samples with narrowband vibronic features. 

"These two exemplary works showcase her ability to innovate upon complex spectroscopic techniques in order to provide valuable information on excited state reaction dynamics in highly multidimensional systems," said Frontiera.

Based on the success with her initial rubrene project, Kajari initiated a collaboration with Professor Douglas to examine tailored molecular derivatives of rubrene. She has carefully designed a series of structural derivatives to test specific hypothesis about charge density motion in crystalline rubrenes during singlet fission. She is currently examining these newly synthesized samples and putting together a paper on the comprehensive photophysics of rubrene singlet fission. 

In addition to her research, Kajari is an active-student leader. She is a laboratory safety officer and a member of the department's Joint Safety Team. She is regular volunteer with the Energy and U program, is an outstanding teaching assistant, and was voted chair for the Vibrational Spectroscopy Gordon Research Seminar.

Kajari earned her bachelor's degree in chemistry from the Indian Institute of Science Education and Research Bhopal, India, and a master's degree from the University of Minnesota.

Samuel "Sam" Stoneburner

Samual Stoneburner
Samuel Stoneburner
Sam began working with his adviser Professor Laura Gagliardi as an undergraduate. He was involved in the design of a novel metal-organic framework (MOF) with enhanced back bonding for the separation of N2 and CH4. Sam performed some calculations on a Fe-compound, which is a model for the metal-organic framework Fe-MOF-74. He studied the binding of this model compound to N2 and CH4. He also was co-author of a paper on this topic.

Sam's main project as a graduate student concerns the study of binding of NO, CO2 and N2 to mono-catecholate metal moieties that ideally can be inserted into a MOF. He reported some unexpected results on the relative binding on N2 versus CO2, which has attracted the attention of experimental colleagues. He is focusing on air separation using metal catecholate, screening the entire periodic table to find promising metals for this separation, and employing different electronic structure theories to address this challenge. Sam's research generated a second paper in this area with special focus on the use of metal catecholates for air separation.

In the area of gas separations, Sam has investigated metal organic frameworks containing a copper paddle-wheel building unit. This project was performed as a collaboration between Professor Gagliardi's group and the group of Professor Berend Smit at École polytechnique fédérale de Lausanne, Switzerland. Sam performed electronic structure calculations needed for this project, showing that density functional theory methods severely underestimate the interaction energy between copper paddle wheels and CO2, even including corrections for the dispersion forces. In contrast, a multireference wave function followed by perturbation theory to second order using correctly describes this interaction.

Another area of research for Sam is the development and testing of methods based on multireference wave functions. In his first project in this area, published in the Journal of Chemical Theory and Computation, he explored the applicability and accuracy of generalized active space self-consistent field methods. He computed the electronic excitation energies of several molecules, including ozone, furan, pyrrole, nickel dioxide, and copper tetrachloride dianion. His contribution provided general guidelines for the optimum applicability of these methods with their current limitations. He has explored the systematic design of active spaces for multi-reference calculations of singlet–triplet gaps of organic diradicals, to be utilized in conjunction with multi-configuration pair-density functional theory, a method recently developed by Professor Gagliardi and Professor Donald Truhlar's groups. This study has generated two papers published in the Journal of Chemical Physics in 2017 and 2018. Currently, Sam is working to understand how to improve the performance of multireference methods for systems containing transition metals.

Sam is a leader in Professor Gagliardi's research group, mentoring undergraduates and high school students working in her group. He is a natural teacher, and is involved in the University of Minnesota's Mentorship Program for Aspiring Chemistry Teachers. As part of this program, Sam helped Professor Gagliardi teach the elementary quantum mechanics course. After earning his doctorate this spring, Sam will start as a chemistry professor at Messiah College in Pennsylvania.

Sam earned an associate of applied science in chemical technology from the Kalamazoo Valley Community College in Michigan, a Bachelor of Science in chemistry and mathematics from Hillsdale College in Michigan, and a Master of Science in chemistry from the University of Minnesota.