Chemical Physics and Physical Chemistry

Physical Chemistry Seminar: Dr. Antoine Kahn, Princeton University

Thu, 2018-11-08 13:00 - 14:00
Speaker: 
Dr. Antoine Kahn
" Electron spectroscopy and the study of metal halide perovskite surfaces and interfaces"

 

 

  

 The formidable promises of the “re-discovered” class of organic/inorganic metal halide perovskites (MHP) such as methylamonium lead tri-iodide (MAPbI3), and the rapid and steady rise in device performance achieved with these materials over the past seven years, have triggered a flurry of research all over the world. This talk reviews our efforts to understand key surfaces and interfaces of these materials. We first report a combined ultra-violet/inverse photoemission spectroscopy (UPS/IPES) - DFT study of the surface electronic structure of several 3D-MHPs, e.g., MAPbI3, MAPbBr3, and CsPbBr3, which yield valence and conduction band edge positions (VBM, CBM), ionization energy and electron affinity (IE, EA), energy gap. An unusually low density of states is found at the VBM of these materials, with potential consequences on device physics. We then look at recent measurements of the electronic structure of MHP interfaces with hole and electron transport layers used for carrier extraction/blocking in photovoltaic devices. Specifically, the role of p-doping is investigated in the case of interfaces between the HTL poly(triarylamine) (PTAA) and CsPbBr3.  We then turn to two-dimensional metal halide perovskites (2D-MHP) and present electronic structure measurements on several 2D butylammonium methylammonium lead iodide and bromide compounds, BA2MAn-1PbnI3n+1, n=1 - 4. XRD, AFM, UV-vis absorption, and UPS/IPES spectroscopies are used to investigate these compounds.  Their single-particle gap is obtained from UPS/IPES results, and compared with optical absorption measurements to deduce an exciton binding energy (EB). In agreement with previous results, EB is found to be large for n=1 and 2 (390 and 110 meV, respectively), but drops rapidly for n=3 and above. Finally, a simple model is presented to justify the electron and hole levels and the single particle gap in these quantum wells structures.  

 

Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Host: Dr. Rappe

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Tom Miller, Caltech

Thu, 2018-10-18 13:00 - 14:00
Speaker: 

Dr. Tom Miller

 

 

Getting Something For Nothing:

Classical and Machine-Learning Methods for Quantum Simulation

 


 

A focus of my research is to the develop simulation methods that reveal the mechanistic details of quantum mechanical reactions that are central to biological, molecular, and heterogenous catalysis. The nature of this effort is three-fold: we work from the foundation of quantum statistical mechanics and semiclassical dynamics to develop methods that significantly expand the scope and reliability of condensed-phase quantum dynamics simulation; we develop quantum embedding and machine learning methods that improve the description of molecular interactions and electronic properties; and we apply these methods to understand complex chemical systems.

The talk will focus on recent developments [1] and applications [2] of Feynman path integral methods for the description of non-adiabatic chemical dynamics, including proton-coupled electron-transfer and long-ranged electron transfer in protein systems.  Additionally, we will describe a machine-learning approach [3] to predicting the electronic structure results on the basis of simple molecular orbitals properties, yielding striking accuracy and transferability across chemical systems at low computational cost.

 

[1] "Path-integral isomorphic Hamiltonian for including nuclear quantum effects in non-adiabatic dynamics." X. Tao, P. Shushkov, and T. F. Miller III, J. Chem. Phys., 148, 102327 (2018).

 

[2] "Fluctuating hydrogen-bond networks govern anomalous electron transfer kinetics in a blue copper protein." J. S. Kretchmer, N. Boekelheide, J. J. Warren, J. R. Winkler, H. B. Gray, and T. F. Miller III, Proc. Natl. Acad. Sci. USA, 115, 6129 (2018).

 

[3] "Transferability in machine learning for electronic structure via the molecular orbital basis." M. Welborn, L. Cheng, and T. F. Miller III, J. Chem. Theory Comput., in press, DOI: 10.1021/acs.jctc.8b00636.
Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Host: Dr. Subotnik

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Jeanne Stachowiak, University of Texas- Austin

Thu, 2018-10-04 13:00 - 14:00
Speaker: 

Dr. Jeanne Stachowiak

 

" Stochastic Mechanisms in Membrane Traffic"

-Membrane traffic, an essential cellular process that plays a role in many human diseases, requires key biophysical steps including formation of membrane buds, loading of these buds with specific molecular cargo, separation from the parent membrane, and fusion with the target membrane. The prevailing view has been that structured protein motifs such as wedge-like amphipathic helices, crescent-shaped BAR domains, curved coats and constricting dynamin rings drive these processes. However, many proteins that contain these structural motifs also contain large intrinsically disordered protein (IDP) domains of 300-1500 amino acids, including many clathrin and COPII coat components. While these IDP domains have been regarded primarily as flexible biochemical scaffolds, we have recently discovered that IDPs are highly efficient physical drivers of membrane budding. Further, our work demonstrates that IDP domains serve as strong drivers of membrane fission. How can molecules without a defined structure drive membrane budding and fission? Our results support the idea that disordered domains generate entropic pressure at membrane surfaces, which is critical to overcoming key biophysical barriers to membrane traffic. IDPs are particularly efficient generators of entropic pressure owing to their very large hydrodynamic radii, potential for electrostatic repulsion owing to high net charge, and the substantial entropic cost of extending them. More broadly our findings suggest that any protein,regardless of structure, can contribute to membrane remodeling by increasing entropic pressure, and paradoxically, that proteins that lack a defined secondary structure, IDPs, may be among the most potent drivers of membrane traffic. Our ongoing work focuses on understanding how entropic pressure influences membrane traffic, and designing biophysical tools for manipulating receptor recycling and signaling.
Location: 

Carol Lynch Lectrue Hall

Chemistry Complex

Host: Dr. Baumgart

 inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Paul Cremer, Pennsylvania State University

Thu, 2018-09-20 13:00 - 14:00
Speaker: 

Dr. Paul Cremer

" Probing the Interactions of Ions and Small Molecules with Phospholipid Membranes"

The interactions of ions and small molecules with lipid head groups depends intimately on the structure of the analytes and the chemical composition of the membrane. In this talk, it will be shown that these interactions can be facilely probed by fluorescence microscopy when using a pH sensitive probe. The ability of small organic species to insert into the membrane depends on the charge on the membrane, the charge on the small molecule, the presence of cholesterol, as well as the presence of other specific membrane lipids (e.g. phosphatidylethanolamine or phosphatidylglycerol). Further information on the insertion process can be obtained from sum frequency generation (SFG), Langmuir isotherm, and fluorescence recovery after photobleaching (FRAP) measurements. Intriguingly, it is revealed that the perturbation of the interfacial water structure can be correlated with the mechanisms of small molecule-membrane interactions under certain conditions. These types of interactions are significant because soluble drug molecules typically are meant to interact with specific protein receptors and membrane-drug interactions present an additional and often unintended influence.

 

 

Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Attached Document: 

Host: Dr. Gai

 

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Akbar Salam, Wake Forest

Thu, 2018-09-06 13:00 - 14:00
Speaker: 

Dr. Akbar Salam

 Molecular QED Theory of Resonance Energy Transfer 

 

 Abstract: The fundamental theory of electron-photon interactions is quantum electrodynamics (QED). Its characteristic feature is the quantisation of the electromagnetic field. One of the successes of the molecular version of QED [1,2] is the unified description it provides of resonance energy transfer (RET) [1]. This process is viewed as arising from the exchange of a single virtual photon between an initially excited donor species and a ground state acceptor moiety. Asymptotic limits of the Fermi golden rule transition rate reveal a radiationless Förster type of exchange mechanism in the near-zone that has inverse sixth power separation distance dependence, and a radiative inverse square law behaviour at large displacements.

 

 

 

In this seminar an overview of the theory of molecular QED and its application to pair RET will be given first, before recent results are presented concerning the role that one and two additional passive polarisable molecules have in modifying the transfer rate [3,4]. Insight is gained into migration of energy in an environment of bath molecules by comparing these microscopic models of RET occurring between individual particles with a polariton based approach [5] in which direct excitation energy transfer is facilitated by medium-dressed photons.

 

 

 

[1] A. Salam, Molecular Quantum Electrodynamics, John Wiley & Sons, Inc., Hoboken, 2010.

 

[2] D. L. Andrews, G. A. Jones, A. Salam and R. G. Woolley, J. Chem. Phys. 148, 040901 (2018).

 

[3] A. Salam, J. Chem. Phys. 136, 014509 (2012).

 

[4] D. L. Andrews and J. S. Ford, J. Chem. Phys. 139, 014107 (2013).

 

[5] G. Juzeliunas and D. L. Andrews, Adv. Chem. Phys. 112, 357 (2000). 

 

 

Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Attached Document: 

Host: Dr. Nitzan and Subotnik

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. John Mauro, Pennsylvania State University

Thu, 2018-08-30 13:00 - 14:00
Speaker: 

Dr. John Mauro

Relaxation is Everywhere
As a nonequilibrium material, a glass is continually relaxing towards its metastable supercooled liquid state.  A comprehensive understanding of glass relaxation is of critical importance for many high-tech applications of glass, including optical fiber, glass substrates for liquid crystal displays, and chemically strengthened cover glass for electronic devices.  In this presentation, I will review the current state-of-the-art in understanding the dynamics of glass relaxation, including the physical origins of its non-Arrhenius and non-exponential characters
Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Host Dr. Fakhraai

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Herr vander Zant, (TUDelft)

Mon, 2018-04-23 15:00 - 16:00
Speaker: 
Host:Gai
Location: 
Carol Lynch Lecture Hall Chemistry Complex

Single-molecule quantum transport for electronic component s

 


Physical Chemistry Seminar: Dr. Alexander Sodt (NIH/ NICHD)

Thu, 2018-03-01 13:00 - 14:00
Speaker: 
Host: Baumgart
Location: 
Carol Lynch Lecture Hall Chemistry Complex

Title: Simulating and modeling the molecular mechanisms of biological lipid membrane reshaping

 

Physical Chemistry Seminar, Dr. David Osborn(Sandia National Laboratories)

Thu, 2018-04-26 13:00 - 14:00
Speaker: 
Host: Lester
Location: 
Carol Lynch Lecture Hall Chemistry Complex
Attached Document: 

Title: “Autoxidation chemistry driven by isomerizations:  the direct observation of a hydroperoxy alkyl radical"

 

Physical Chemistry Seminar, Dr. Xueming Yang( Dalian Institute of Chemical Physics)

Wed, 2017-12-06 12:00 - 13:00
Speaker: 
Host: Lester
Location: 
Carol Lynch Lecture Hall Chemistry Complex

Surface Photocatalysis of Methanol and Water at Single Molecule Level

Department of Chemistry

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