8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P3.40Fri 911:10-14:00Multiscale simulation of rod-like liquid crystalsIori Yonekawa 1 and Kenji Yasuoka 11 Keio University, 3-14-1, Hiyoshi, Kohoku-ku, , Yokohama-shi, Kanagawa-ken 223-8522,Yokohama, JapanTo reveal characters of liquid crystals, molecular dynamics (MD) simulation can be a powerfultool. So far, many MD simulations of liquid crystals have been reported. Some are atomistic MD,and some are coarse-grained (CG) MD. But both of them are insufficient to simulate the phase transitionof liquid crystals, which happen at 100ns order timescale and cause conformational changein molecules. Atomistic MD requires extremely large calculation cost and CG MD cannot considerconformational change. Therefore, merits and demerits of these MDs have a trade-off. In thisstudy, we developed the multiscale simulation method using both atomistic and CG models. Westudy rod-like liquid crystals. Our first target is 5CB (4-pentyl-4’-cyanobiphenyl). 5CB is one ofthe simplest nematic liquid crystals. We used OPLS-UA (UA) model as atomistic model, and Gay-Berne (GB) model as CG model. In the GB model, we used one molecule as modeled one uniaxialellipsoid and used Gay-Berne potential, which is a modified form of Lennard-Jones potential. Ourmethod of multiscale simulation is parameter-update style. In general CG simulation, parametersare calculated only once before running a simulation. This is why CG MD cannot simulate phasetransition of liquid crystals well. So in our method, we renewed GB parameters by UA-MD in thesimulation. We renewed ? and ?0, which determine the shape of the GB particle and have a largeeffect on the phase diagram. To calculate these parameters, we used the principle of equipartition.We calculated translate temperature and rotational temperature of the UA system (calculated byimaginary GB parameters). We determined new GB parameters so that ensemble averages of thesetemperatures are equal. We simulated both heating and cooling processes of 5CB. Our methodcan closely estimate phase transition temperature between isotropic and nematic phase of 5CB andachieve 100 times acceleration over UA-MD.40