Speaker: John Sous, (University of British Columbia)
Date: Thursday, November 9th
Time: 12:00-1:00 pm
Includes Pizza.
Title: Phonon-mediated repulsion, sharp transitions and (quasi)self-trapping in the extended Peierls-Hubbard model
Abstract: Particle-phonon coupling is generically expected to lead to a screening of the bare particle-particle interactions. If low-energy overscreening occurs, the resulting attractive interactions are responsible for conventional superconductivity as described by the Bardeen-Cooper-Schrieffer theory. I will demonstrate that Peierls-type particle-phonon coupling not only leads to an enhanced repulsion between identical fermions/hard-core bosons, but also generates an additional effective interaction not of density-density type and thus not involved in screening. This interaction moves pairs of neighbor particles as a whole; this has unusual consequences such as a (quasi)self-trapping transition for a bound pair even when the individual particles are very mobile. These results open new directions in the study and understanding of the effects of particle-boson coupling, relevant for understanding behavior in Physics, e.g. in quantum materials; Chemistry, e.g. in optoelectronic processes; and Biology, e.g. in photosynthesis and DNA.
Location: B-106 @ Center for Astrophysics (60 Garden Street)
Directions: After entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, B-106 will be at the end of the hallway on the left side.
Dear students and postdocs,
tomorrow, Wednesday, November 15th, we will take this week’s ITAMP/HQOC speaker Tongcang Li out for lunch at Russel House Tavern. If you would like to join, please sign up via the following link (limited to 8 people):
https://docs.google.com/spreadsheets/d/1aY3B6-XNLVZFr6iX502cG36IuJ7IFTKp6Pf…
We meet at LISE cafe at 11:40.
Best,
Hannes
Hi everyone,
Tobias Kramer will give a Seminar this Friday at 2pm in the division room.
Please find below Tobias' title and abstract.
Cheers Christoph
Title: Bringing HEOM up-to-speed on a supercomputer
Abstract:
I present our current work to provide a scalable open quantum system
dynamics using HEOM for supercomputers with hundreds of nodes. At the
Zuse-Institute Berlin (ZIB) we implement the Hierarchical Equations of
Motion (HEOM) method and provide utilities to compute various optical
response functions. As illustration I compare computed 2D spectra with
experiments of the photosynthetic apparatus of C. Tepidum [1] for various
polarization sequences.
References:
[1] Tobias Kramer, Mirta Rodriguez: Two-dimensional electronic spectra of
the photosynthetic apparatus of green sulfur bacteria
Scientific Reports, Vol.7, p. 45245, 2017
Everyone,
If you are traveling with Alan to Glasgow for the visit to the Cronin Group
February 11-13. Come see me now, before 4 PM or tomorrow morning after 11
AM.
Cheers,
Siria
--
*Siria Serrano*
*Faculty Assistant*
*Aspuru-Guzik Group*
*Harvard University **Department of Chemistry and Chemical Biology*
*12 Oxford St. M 136*
*Cambridge, MA 02138*
*P:** (617) 496-1716 <%28617%29%20496-1716>** F: **617-496-9411
<617-496-9411>*
*ITAMP Lunch Seminar*
*Speaker:* Yehuda B. Band (Ben-Gurion University)
*Date:* Monday, Jan 29th
*Time:* 12:00-1:00 pm
Includes Pizza.
*Title: *Dynamics of a Magnetic Needle Magnetometer: Sensitivity to
Landau-Lifshitz-Gilbert Damping and External Noise Decoherence
*Abstract: *We analyze the dynamics of a single-domain magnetic needle,
which can be used as a high precision magnetometer. We determine the
uncertainty of the magnetometer due to Gilbert dissipation and the
associated internal magnetic field fluctuations. We then discuss the
effect of external magnetic noise. We also consider needle dynamics in an
inhomogeneous magnetic field (e.g., a Ioffe-Pritchard trap) and discuss
magnetic levitation and stability.
*Location: *B-106 @ Center for Astrophysics (60 Garden Street)
*Directions: *After entering the lobby of the CfA, turn right to enter the
hallway of the B building. In the hallway, turn right again, B-106 will be
at the end of the hallway on the left side.
Hi All,
We will have a visit of postdoc candidate next Monday. The abstract of the talk is pasted below. Please let me know if you want to meet with her and/or have a lunch (12pm-1:30pm) on Monday.
Cheers,
Dennis
Accurate treatment of charge-transfer excitations and thermally activated delayed fluorescence using the particle-particle random phase approximation
Abstract: Thermally-activated delayed fluorescence (TADF) is a mechanism that increases the efficiency of light emission in organic light-emitting diodes by harnessing both singlet and triplet excitons. TADF is facilitated by a small energy difference between the first singlet (S1) and triplet (T1) excited states [*E(ST)], which is minimized by spatial separation of the donor and acceptor moieties. The resultant charge-transfer (CT) excited states are difficult to model using semilocal exchange-correlation (xc) functionals combined with time-dependent density functional theory because of the delocalization error present in these approximate methods. In this talk I will review approaches to model CT transitions in TADF emitters and introduce the results from the particle-particle random phase approximation (pp-RPA). The pp-RPA is able to capture CT states and accurately reproduce excitation energies which is attributed to the consistent treatment of both ground and excited states. Qualitative characterization of excited states as CT or locally excited, in comparison with experiment, and interesting structural features of TADF molecules will be discussed as well.
Speaker: Rachael Al-Saadon
---------- Forwarded message ---------
From: Payel Das <daspa(a)us.ibm.com>
Date: Mon, Jan 22, 2018 at 4:11 PM
Subject: 2018 IBM Social Good Fellowship program
To: <alan(a)aspuru.com>
Hi Alan,
Hope this email finds you well. You may remember that I mentioned to you
about the IBM Social Good Fellowship program during our meeting at IBM
Watson. Could you please share the announcement within your team,
department and any one who might be interested in applying? Although the
deadline has passed, we are still accepting applications for 2018.
Thanks and regards,
Payel
The IBM Science for Social Good initiative is an opportunity for graduate
students to develop their skills and develop artificial intelligence-based
solutions that benefit humanity. Mentored by leading IBM Research
scientists and engineers at the T. J. Watson Research Center in Yorktown
Heights, NY (north of New York City), fellows use artificial intelligence
and machine learning methods to complete projects with social impact.
Working closely with non-governmental organizations, social enterprises,
government agencies, and other mission-driven partners, fellows take on
real-world problems in health, energy, environment, education,
international development, equality, justice, and more.
More info can be found at:
https://www.research.ibm.com/science-for-social-good/
Apply by January 15 to: https://ibm.biz/Bdj9iV
------
Payel Das, Ph.D.
Research Staff Scientist and Technical Lead
Data Science and Cognitive Computing Department
IBM Thomas J. Watson Research Center
Yorktown Heights, NY 10598
Ph:914-945-2373
Webpage: https://researcher.ibm.com/researcher/view.php?person=us-daspa
--
Alán Aspuru-Guzik | Professor of Chemistry and Chemical Biology
Harvard University | 12 Oxford Street, Room M138 | Cambridge, MA 02138
(617)-384-8188 | http://aspuru.chem.harvard.edu | http://about.me/aspuru
---------- Forwarded message ----------
From: Ikerbasque <ikerbasque(a)ikerbasque.net>
Date: Mon, Jan 22, 2018 at 4:16 AM
Subject: Ikerbasque: 20 Positions for postdoctoral researchers
To: aspuru.staff(a)gmail.com
*Ikerbasque, * the Basque Foundation for Science, would like to inform you
that we have launched *a new international call* to reinforce research and
scientific career in the Basque Country. We offer:
- *20 positions for Promising Researchers* *Ikerbasque Research Fellows*
- 5 year contracts
- PhD degree between Jan2007-Dec2015
- Support letter from the host group is mandatory
- Deadline: March 15th at 13:00 CET
For further information, please visit *calls.ikerbasque.net
<http://calls.ikerbasque.net>*
We would appreciate your help in disseminating this information, in case
you know about any colleague that could be interested and meets the
requirements of the call.
*IKERBASQUE*
*Basque Foundation for Science*
To unsubscribe from this group, please send us an email to
ikerbasque(a)ikerbasque.net
Podrá ejercitar su derecho de acceso, rectificación, cancelación y
oposición mediante envio de un correo electrónico a la siguiente dirección
ikerbasque(a)ikerbasque.net
--
*Siria Serrano*
*Faculty Assistant*
*Aspuru-Guzik Group*
*Harvard University **Department of Chemistry and Chemical Biology*
*12 Oxford St. M 136*
*Cambridge, MA 02138*
*P:** (617) 496-1716 <%28617%29%20496-1716>** F: **617-496-9411
<617-496-9411>*
[image: Inline image 1]
Oreos available in the office! Feel free to swing by and grab some.
*Felixander Negron*
*Laboratory Administrator *
*Aspuru-Guzik Group*
*Harvard University *
*Department of Chemistry and Chemical Biology*
*12 Oxford St. M 136*
*Cambridge, MA 02138*
*P:** (617) 496-9964** F: **617-496-9411*
Please post and forward to your group(s).
Excitonics/Perovskite Seminar Tomorrow!
Origins of Delayed Recombination and Halide Segregation in Metal Halide Perovskites*
January 18, 2018 at 12 noon/13-3038
Kyle Frohna
University of Cambridge, UK, Visiting Researcher
[http://www.rle.mit.edu/excitonics/wp-content/uploads/2018/01/frohna-200x300…]
The origin of the long carrier lifetimes in metal-halide perovskites observed at low photoexcitation carrier densities is a hotly debated topic. To date, a variety of mechanisms have been proposed explaining this behavior including: polaron formation, long-lived trap states, as well as the direct-indirect nature of the bandgap, which has been attributed to the Rashba effect. However, the Rashba effect requires the breaking of the centrosymmetric I4/mcm space group, which is a subject of considerable disagreement in the community. We have recently probed the space group of room temperature tetragonal MAPbI3 using second harmonic generation rotational anisotropy (SHG-RA). In this seminar, I will discuss a combination of the SHG-RA measurements, first principles density functional theory calculations, and analytical van Roosbroeck-Shockley calculations to investigate the implications the Rashba effect may have on the radiative lifetime of perovskites.
I will also discuss photo-induced halide segregation, a phenomenon that has been put forward as a potential cause of the reduced performance of wide bandgap, mixed-halide perovskites for tandem solar cells. Large voltage deficits have been observed in these perovskites due to thermalisation of carriers into lower bandgap, iodide-rich regions. By compositionally engineering these perovskites and monitoring their behavior using steady-state photoluminescence and voltage measurements, a new strategy for mitigating halide segregation will be shown.
Kyle Frohna is currently a visiting researcher working with Samuel D. Stranks in the Cavendish Laboratory at the University of Cambridge. He recently completed his undergraduate degree in Nanoscience and Materials Science at Trinity College, Dublin. He has worked previously with Professor Marco Bernardi at the California Institute of Technology on computing the transport properties of carriers in metal halide perovskites and he completed his undergraduate thesis project with Professor Michael McGehee at Stanford University on the fabrication of high efficiency perovskite-silicon tandems.
*This talk is part of the Perovskites Seminar Series organized by Juan-Pablo Correa-Baena from MIT's PV Lab and sponsored by the Center for Excitonics. For more info contact Juan-Pablo: jpcorrea(a)mit.edu<mailto:jpcorrea@mit.edu>
The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S. Department Of Energy,
Office Of Science And Office Of Basic Energy Sciences
Catherine Bourgeois
Program Manager
Assistant to Director
Research Laboratory of Electronics
77 Massachusetts Avenue, Rm: 36-417
Cambridge, MA 02139
P-617-253-0085
F-617-253-1301