Physics Faculty Candidate Colloquium, "First-Principles Study of Redox Reactions: Electron Transfer, Oxidation States and Reactions of a Novel H2-Evolving Electrocatalyst," by Dr. Patrick H-L Sit, Princeton University Friday, 2/17/2012, 4:00 PM-5:00 PM
Quantum mechanical simulations have become powerful tools that provide valuable insight and realistic predictions in the study of important scientific and technological problems due to the ever-increasing computational power and the development of more accurate methodologies. In this talk, I will discuss the study of electron transfer reactions from first-principles simulations. An accurate computational study of electron transfer reactions requires a proper choice of the reaction coordinate, a correct definition of the oxidation states, and a careful consideration of solvent effects on the underlying electron transfer process. I have developed a novel approach to determining oxidation states from first-principles calculations. This approach provides a simple and unambiguous definition of oxidation states, which contributes to the resolution of the long-standing problem of defining oxidation states in quantum mechanical calculations. Using the ferrous-ferric self-exchange reaction in water (Fe2+(aq)+Fe3+(aq)Fe3+(aq)+Fe2+(aq)) as a prototypical example, I have introduced a method to calculate the diabatic free-energy surfaces of electron transfer full reactions using first-principles molecular dynamics (FPMD) simulations. Coupled with an approach to evaluate the electronic coupling parameter, the quantum mechanical estimate of the electron transfer rate is significantly improved. In the second part of the talk, I will report on a recent study of a biologically-inspired H2-producing electrocatalyst. This newly-designed electrocatalyst consists of an active center of di-iron hydrogenase attached directly to a pyrite electrode. A detailed mechanistic understanding of the H2-evolution reaction is obtained through FPMD simulations and the maximally-localized Wannier function analysis technique. The O2 sensitivity of the hydrogenase active center and the eletrocatalyst is also investigated using extensive density-functional calculations and FPMD simulations.
Refreshments will be served in Olin Hall 118 at 3:30 P.M.
Physics Faculty Candidate Colloquium," Colloidal Quantum Dot Photovoltaic," by Dr. Xihua Wang, University of Toronto Wednesday, 2/22/2012, 4:00 PM-5:00 PM
Semiconductor colloidal quantum dots (CQDs), including lead chacolgenide CQDs that have tunable electronic bandgaps from infrared to visible, serve as good candidates to harvest the broad spectrum of sunlight. CQD materials enable multi-junction solar cells using a single material programmed using the quantum size effect. I will present the first CQD tandem solar cells using the size-effect tuning of a single CQD material, PbS. I made such devices by using a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine. The reported tandem solar cell has an open-circuit voltage of 1.06 V, equal to the sum of the two constituent single-junction devices, and a solar power conversion efficiency of up to 4.2%. I will also discuss recent advances in CQD solar cells, including new insights into materials synthesis and processing, as well as thin film physics and device operation, that seek to enable this class of devices to reach their full performance potential.
Refreshments will be served in Olin Hall 118 at 3:30 p.m.
Physics Faculty Candidate Colloquium, "Three-dimensional Analysis of Clathrin-mediated Membrane Trafficking in Living Cells," by Dr. Comert Kural, Harvard Medical Center Thursday, 3/1/2012, 4:00 PM-5:00 PM
Clathrin-coated vesicles are the most prominent carriers of membrane traffic from cell surface to endosomes (endocytosis), a pathway by which hormones, transferrin, immunoglobulins, LDL, viruses, and their receptors enter cells. They are also important for traffic between endosomes and the trans-Golgi network. In this presentation, I will discuss (i) technological and analytical advances that I developed to directly visualize clathrin-mediated membrane traffic in three dimensions and in living cells; (ii) data obtained using these advances that defined a role for actin filament polymerization in counteracting membrane tension during clathrin-coated vesicle budding at the apical surface of polarized epithelial cells; and (iii) how these advances can be used to study a wide variety of biological processes that occur in living cells and tissues.
Refreshments will be served in Olin Hall 118 at 3:30 p.m.
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Physics Faculty Candidate Colloquium, "First-Principles Study of Redox Reactions: Electron Transfer, Oxidation States and Reactions of a Novel H2-Evolving Electrocatalyst," by Dr. Patrick H-L Sit, Princeton University Friday, 2/17/2012, 4:00 PM-5:00 PM
Quantum mechanical simulations have become powerful tools that provide valuable insight and realistic predictions in the study of important scientific and technological problems due to the ever-increasing computational power and the development of more accurate methodologies. In this talk, I will discuss the study of electron transfer reactions from first-principles simulations. An accurate computational study of electron transfer reactions requires a proper choice of the reaction coordinate, a correct definition of the oxidation states, and a careful consideration of solvent effects on the underlying electron transfer process. I have developed a novel approach to determining oxidation states from first-principles calculations. This approach provides a simple and unambiguous definition of oxidation states, which contributes to the resolution of the long-standing problem of defining oxidation states in quantum mechanical calculations. Using the ferrous-ferric self-exchange reaction in water (Fe2+(aq)+Fe3+(aq)Fe3+(aq)+Fe2+(aq)) as a prototypical example, I have introduced a method to calculate the diabatic free-energy surfaces of electron transfer full reactions using first-principles molecular dynamics (FPMD) simulations. Coupled with an approach to evaluate the electronic coupling parameter, the quantum mechanical estimate of the electron transfer rate is significantly improved. In the second part of the talk, I will report on a recent study of a biologically-inspired H2-producing electrocatalyst. This newly-designed electrocatalyst consists of an active center of di-iron hydrogenase attached directly to a pyrite electrode. A detailed mechanistic understanding of the H2-evolution reaction is obtained through FPMD simulations and the maximally-localized Wannier function analysis technique. The O2 sensitivity of the hydrogenase active center and the eletrocatalyst is also investigated using extensive density-functional calculations and FPMD simulations. Refreshments will be served in Olin Hall 118 at 3:30 P.M.
Physics Faculty Candidate Colloquium," Colloidal Quantum Dot Photovoltaic," by Dr. Xihua Wang, University of Toronto Wednesday, 2/22/2012, 4:00 PM-5:00 PM
Semiconductor colloidal quantum dots (CQDs), including lead chacolgenide CQDs that have tunable electronic bandgaps from infrared to visible, serve as good candidates to harvest the broad spectrum of sunlight. CQD materials enable multi-junction solar cells using a single material programmed using the quantum size effect. I will present the first CQD tandem solar cells using the size-effect tuning of a single CQD material, PbS. I made such devices by using a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine. The reported tandem solar cell has an open-circuit voltage of 1.06 V, equal to the sum of the two constituent single-junction devices, and a solar power conversion efficiency of up to 4.2%. I will also discuss recent advances in CQD solar cells, including new insights into materials synthesis and processing, as well as thin film physics and device operation, that seek to enable this class of devices to reach their full performance potential. Refreshments will be served in Olin Hall 118 at 3:30 p.m.
Physics Faculty Candidate Colloquium, "Three-dimensional Analysis of Clathrin-mediated Membrane Trafficking in Living Cells," by Dr. Comert Kural, Harvard Medical Center Thursday, 3/1/2012, 4:00 PM-5:00 PM
Clathrin-coated vesicles are the most prominent carriers of membrane traffic from cell surface to endosomes (endocytosis), a pathway by which hormones, transferrin, immunoglobulins, LDL, viruses, and their receptors enter cells. They are also important for traffic between endosomes and the trans-Golgi network. In this presentation, I will discuss (i) technological and analytical advances that I developed to directly visualize clathrin-mediated membrane traffic in three dimensions and in living cells; (ii) data obtained using these advances that defined a role for actin filament polymerization in counteracting membrane tension during clathrin-coated vesicle budding at the apical surface of polarized epithelial cells; and (iii) how these advances can be used to study a wide variety of biological processes that occur in living cells and tissues. Refreshments will be served in Olin Hall 118 at 3:30 p.m.
Powered by the Social Web - Bringing people together through Events, Places, & Common Interests