Ab initio molecular polarisabilities of liquid crystals:: Application to DOBAMBC and 5CB

We develop and implement a direct computational method to obtain the structure and complete molecular electronic polarisability tensor directly from the first-principles-derived electron charge distributions of mesogens based on a plane-wave basis set approach. In our methods no semi-empirical bond polarisabilities or additivity approximations are introduced. We have chosen two prototypical liquid crystal forming molecules to illustrate the methods. The polarisability for (4-4')-pentyl-cyano-biphenyl (5CB) is found to be in excellent agreement with available experimental data. We also present the molecular dipole, quadrupole and polarisability tensor for the ferroelectric liquid crystal molecule [p-(n-decyloxy-benzylidene)-p-amino-(2-methyl-butyl)] cinnamate (DOBAMBC). For 5CB, Ne compare calculated polarisabilities obtained from our density functional plane-wave method with those based on localised basis set techniques. We find that the polarisability is generally overestimated by the localised basis methods and that the results do not necessarily converge with increasing localised basis set sophistication.