A computer simulation study of tilted smectic mesophases

Abstract

Comment on "Monte Carlo simulations of smectic phase transitions in flexible-rigid-flexible molecules" [J. Chem. Monte Carlo study of a semiflexible liquid crystal model: The smectic phaseWe present comprehensive results from constant NVT and constant NPT Monte Carlo simulations of particles interacting via a biaxial variant of the Gay-Berne potential which we term the Internally Rotated Gay-Berne ͑IRGB͒ potential. The IRGB potential may be considered to be a single-site approximation to the interaction between two zig-zag shaped molecules, the extent of this molecular biaxiality being characterized by an internal rotation angle ␦. We find that increasing the value of ␦ frustrates the formation of orientationally ordered phases, all phase transitions being shifted to lower temperatures and higher densities. Additionally, for ␦у30 degrees, the smectic B phase is replaced by the tilted smectic J phase. The smectic A phase, in contrast, is destabilized completely for sufficiently large ␦, with neither smectic A nor its tilted equivalent, smectic C, being observed. This suggests that models for smectic C-formation which are based on biaxial intermolecular attractions may not offer the best route to obtaining this phase.

Shape segregation in molecular organisation: a combined X-ray scattering and molecular dynamics study of smectic liquid crystals

“…For each trajectory frame, the layer normal was defined using a method described in the literature, 85,86 and was obtained by diagonalising a tensor of local layer normals generated from all N molecules, using an equation equivalent to eqn (1) but with the component of the local layer normal l replacing a. The local layer normal at each molecule was determined by selecting a suitable reference position within the molecule, defined in the text, generating a plane by an RMS fit centred on that point and including all equivalent points in other molecules within a cut-off distance of 1 nm, and then calculating the vector normal to this plane.…”

Time reversible and symplectic integrators for molecular dynamics simulations of rigid molecules

“…Note that in the case here the normal to the layer coincide with director n and in the case that the normal to the layer of smectic phases is not parallel to n another technique should be adopted to calculate g ʈ ͑r ʈ ͒ and g Ќ ͑r Ќ ͒. 48 In analysis of a smectic layer we calculated the correlation function g 6 ͑r Ќ ͒ which allows us to distinguish between smectic phases such as the SmA and SmB. 49 The bond correlation function g 6 ͑r Ќ ͒ is given by g 6 ͑r Ќ ͒ = ͗ 6 ͑r i ͒ 6 ͑r i ͒͘, ͑B6͒…”

An insight into de Vries behaviour of smectic liquid crystals from atomistic molecular dynamics simulations

“…59,74 The simulation layer normal, k, calculated at each trajectory frame, was obtained by determination of a local layer normal for each molecular reference position, i, followed by diagonalisation of the associated ordering tensor, again as reported previously. 103,104 The layer spacing, d, was defined as the distance corresponding to the maximum density fluctuation of the molecular reference positions along the calculated layer normal. The carbon atom on the central aromatic ring, closest to the 9-carbon aliphatic chain was defined as the position of the molecular centre of 9HL.…”