Abstract
The physical properties and phase transitions of thermotropic liquid crystals are highly sensitive to small changes in chemical structure. However, these changes are challenging to model, as both the phase diagram and mesophase properties obtained from fully atomistic simulations are strongly dependent on the force field model employed, and the current generation of chemical force fields has not proved accurate enough to provide reliable predictions of transition temperatures for many liquid crystals. This paper presents a strategy for improving the nematic clearing point, TNI, in atomistic simulations, by systematic optimization of the General Amber Force Field (GAFF) for key mesogenic fragments. We show that with careful optimization of the parameters describing a series of liquid crystal fragment molecules, it is possible to transfer these parameters to larger liquid crystal molecules and make accurate predictions for nematic mesophase formation. This new force field, GAFF-LCFF, is used to predict the nematic-isotropic clearing point to within 5 °C for the nematogen 1,3-benzenedicarboxylic acid,1,3-bis(4-butylphenyl)ester, an improvement of 60 °C over the standard GAFF force field.
Highlights
Over the last few years, computer simulations techniques have proved immensely useful in the study of thermotropic liquid crystals.[1,2] Simulation studies have provided a series of insights into the structure and dynamics of liquid crystal phases over a wide range of time and length scales
Coarse-grained models are suitable for the study of large system sizes at reasonably low computational cost, fully atomistic simulations have the potential to link chemical details with the physical properties of a system.[4]
The position and conformation of the ester group is implicated in the development of spontaneous polarization in ferroelectric liquid crystal phases and spontaneous chiral segregation of bent-core liquid crystals as well as affecting the magnitude of the bend angle.[41,42,43,44]
Summary
Over the last few years, computer simulations techniques have proved immensely useful in the study of thermotropic liquid crystals.[1,2] Simulation studies have provided a series of insights into the structure and dynamics of liquid crystal phases over a wide range of time and length scales These include director modelling, and coarse-grained and atomistic molecular models.[1,3] coarse-grained models are suitable for the study of large system sizes at reasonably low computational cost, fully atomistic simulations have the potential to link chemical details with the physical properties of a system.[4] For example, the phase transition temperatures and the stability of a range of mesophases are sensitive to small changes in chemical structure. The phase diagram and mesophase properties derived from atomistic simulations are strongly dependent on the force field employed and its description of the molecular geometry
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