Eur. Phys. J. E 4, 85-91
Structure and elastic properties of a nematic liquid crystal: A theoretical treatment and molecular dynamics simulation
A.V. Zakharov and A. Maliniak.Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm, Sweden arnold.maliniak@physc.su.se
(Received 22 March 2000 and Received in final form 9 June 2000)
Abstract
The Frank elasticity constants which describe splay (K1),
twist (K2), and bend (K3) 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
Ki (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.
61.30.-v - Liquid crystals.
61.30.Cz - Theory and models of liquid crystal structure.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
