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SUMMARY:Distinction of disorder\, classical and quantum vibrational contri
 butions to atomic mean-square amplitudes in dielectric pentachloronitroben
 zene - Jacqui Cole (Structure and Dynamics)
DTSTART:20110216T112000Z
DTEND:20110216T120000Z
UID:TALK28042@talks.cam.ac.uk
CONTACT:Dubois Simon
DESCRIPTION:The solid-state molecular disorder of pentachloronitrobenzene 
 (PCNB) and its role in causing anomalous dielectric properties are investi
 gated. Normal coordinate analysis (NCA) of atomic mean square displacement
  parameters (ADPs) is employed to distinguish disorder contributions from 
 classical and quantum mechanical vibrational contributions. The analysis r
 elies on multi-temperature (5-295K) single-crystal neutron diffraction dat
 a. Vibrational frequencies extracted from the temperature dependence of th
 e ADPs are in good agreement with THz spectroscopic data. The static disor
 der revealed by this work\, primarily tilting and displacement of the mole
 cules\, is compared with corresponding results from previous\, much more i
 n-depth and time-consuming Monte Carlo (MC) simulations\; all their salien
 t findings are reproduced by this work\, demonstrating that the faster NCA
  approach is reliable. The dielectric properties of PCNB can thus be ratio
 nalised by an interpretation of the temperature dependent ADPs in terms of
  thermal motion and molecular disorder. The use of atomic displacement par
 ameters in the NCA approach is nonetheless hostage to reliable neutron dat
 a. The success of this study demonstrates that state-of-the-art single-cry
 stal Laue neutron diffraction affords sufficiently fast the accurate data 
 for this type of study. In general terms the validation of this work opens
  up the field for numerous studies of solid-state molecular disorder in or
 ganic materials.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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