The properties of discotic mesophases are determined by the interactions of molecules forming mesophases. It is difficult to do quantum chemical calculation on so large molecule pairs. Various level calculations have been performed on pairs of benzene derivatives and 1,3,5-benzenetrisamide. The results have been compared with those by high level ONIOM [MP2/6-31G*(0.25):HF/6-31G(d,p)] calculations, finding that the results with ONIOM (HF/STO-3G:AM1:UFF) level calculations are best. The hydrogen bond is dominated by the electrostatic contributions, well covered at the HF/STO-3G level. The stabilization of the stacked molecules was mostly assumed to be due to the dispersion energy, which could be estimated with a UFF method. Triphenyl substituted trimesamide is then optimized at ONIOM (HF/STO-3G:AM1:UFF) level, and the result is in good agreement with the crystallographic data. As an example, 1,3,5-benzenetrisamide with three pendant hexaalkoxytriphenylene groups has been calculated at ONIOM (HF/STO-3G: AM1:UFF) level. The results reported here supported the previous assumption about good charge transfer property of this liquid crystal.

Key words: discotic liquid crystal, charge transfer, quantum chemistry, ONIOM method