Structure and elastic properties of a nematic liquid crystal: A theoretical treatment and molecular dynamics simulation |
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Authors: | AV Zakharov A Maliniak |
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Institution: | (1) Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm, Sweden, SE |
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Abstract: | The Frank elasticity constants which describe splay (K
1), twist (K
2), and bend (K
3) distortion modes are investigated for 4-n-pentyl-4'-cyanobiphenyl (5CB) in the nematic liquid crystal. The calculations
rest on statistical-mechanical approaches where the absolute values of K
i
(i=1,2,3) are dependent on the direct correlation function (DCF) of the corresponding nematic state. The DCF was determined
using the pair correlation function by solving the Ornstein-Zernike equation. The pair correlation function, in turn, was
obtained from molecular dynamics (MD) trajectory. Three different approaches for calculations of the elasticity constants
were employed based on different level of approximation about the orientational order and molecular correlations. The best
agreement with experimental values of elasticity constants was obtained in a model where the full orientational distribution
function was used. In addition we have investigated the approximation about spherical distribution of the intermolecular vectors
in the nematic phase, often used in derivation of various mean-field theories and employed here for the construction of the
DCF. We found that this assumption is not strictly valid, in particular a strong deviation from the isotropic distribution
is observed for short intermolecular distances.
Received 22 March 2000 and Received in final form 9 June 2000 |
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Keywords: | PACS 61 30 -v Liquid crystals - 61 30 Cz Theory and models of liquid crystal structure |
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