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BEGIN:VEVENT
DTSTAMP:20260910T011013Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20081205T170000Z
DTEND:20081205T180000Z
UID:event326@bu.edu
URL:http://physics.bu.edu/internal/events/show/326
SUMMARY:Computing viscosity of supercooled liquids
DESCRIPTION:Featuring Xi Lin\, Boston University\nHosted by: Ophelia Tsui\n
	\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nAbstract:\nWe 
	describe an atomistic method for computing the viscosity of supercooled liq
	uids. A basin-filling algorithm is implemented to sample autonomously the l
	ocal energy minima and saddle points in the potential energy landscape of a
	 binary Lennard-Jones system. Analysis of a sampled trajectory shows the sy
	stem is able to move from one deep minimum to another by a process that inv
	olves high activation energy and the crossing of many local minima and sadd
	le points. Taking this to be the unit event for structural relaxation and u
	sing the relation between average local minimum and temperature from the in
	herent structure concepts of supercooled liquids\, we deduce an effective a
	ctivation barrier that can be used in an expression for the viscosity based
	 simply on transition state theory. We show that this heuristic approach gi
	ves a non-Arrhenius temperature variation matching qualitatively the experi
	mental data on a group of glass-forming liquids classified as fragile. Addi
	tionally we turn to linear response theory where the viscosity is given by 
	the integral of a time-dependent stress correlation function. A network mod
	el describing the hopping between deep minima is formulated and shown to pr
	ovide justification for the preceding heuristic treatment. In a companion p
	aper we report a similar study of silica\, a representative strong liquid. 
	A comparison of the two systems gives insight into the fundamental differen
	ce between strong and fragile scaling.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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