[Crib-list] SPEAKER: Ian Dunn (Columbia University & DOE CSGF Fellow) | Computational Research in Boston and Beyond Seminar (CRIBB) | Thursday, May 30, 2019 | TIME: 12:00 PM - 1:00 PM in Building 32, Room 141 (STATA)

[Shirley Entzminger]

 	               Computational Research in Boston and Beyond Seminar
 				           (CRIBB)

   Notice WEEKDAY of event...


DATE:		Thursday, May 30, 2019

TIME:		12:00 PM to 1:00 PM

LOCATION:	Building 32, Room 141  (STATA)
 		        32 Vassar Street
 		        Cambridge, MA

 		      (Pizza/beverages will be provided at 11:45 AM outside
 		       Room 32-141)


TITLE:		Numerically exact electron-phonon dynamics: projecting
 		 away instabilities in the hierarchical equations
 		 of motion


SPEAKER:	Ian Dunn (Columbia University & DOE CSGF Fellow)


ABSTRACT:

Coupled electron-phonon dynamics span a rich array of chemical and physical
phenomena that includes energy and charge mobility in polar semiconductors,
spectroscopic signatures in organic molecular crystals, dynamics in biological
light-harvesting complexes, and superconductivity. Yet, models of such dynamics
remain challenging to solve. One popular computational approach for solving
these models exactly is the hierarchical equations of motion (HEOM).  We have
found that HEOM contains inherent instabilities that grow exponentially in time.
In the case of continuous-bath models, these instabilities are routinely delayed
to later times by increasing the hierarchy dimension; however, for systems
coupled to discrete, nondispersive modes, increasing the hierarchy dimension
does little to alleviate the problem.  We show that these instabilities can also
be removed completely at a potentially much lower cost via projection onto the
space of stable eigenmodes; furthermore, we find that for discrete-bath models
at zero temperature, the remaining projected dynamics computed with few
hierarchy levels are essentially identical to the exact dynamics that otherwise
might require an intractably large number of hierarchy levels for convergence.
Recognizing that computation of the eigenmodes might be prohibitive, we also
present a Prony filtration algorithm that may be useful as an alternative for
accomplishing this projection when diagonalization is too costly. We present
results demonstrating the efficacy of HEOM projected via diagonalization and
Prony filtration.


===================================================================

Massachusetts Institute of Technology
Cambridge, MA


For information about the Computational Research in Boston and Beyond Seminar
(CRIBB), please visit....

 			http://math.mit.edu/crib/



===

Shirley A. Entzminger
Administrative Assistant II
Department of Mathematics
Massachusetts Institute of Technology
77 Massachusetts Avenue
Building 2, Room 350A
Cambridge, MA 02139
PHONE:	(617) 253-4347
FAX:	(617) 253-4358
E-mail:	daisymae at math.mit.edu
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