[Crib-list] TODAY...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)

[daisymae@mit.edu]

 	T O D A Y . . .


 	                Computational Research in Boston and Beyond Seminar
 				            (CRIBB)



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.


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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