中文摘要：

引入双轴向列相液晶分子模型,采用分叉理论和二粒子集团理论来确定双轴向列相液晶中的Landau点,分别得出了液晶各向同性相向单轴向列相转变对分子双轴性参数的依赖曲线。在Landau点处,分叉理论、二粒子集团理论和平均场理论得到的分子双轴性参数λ取值是相同的,而约化温度t的取值不同,由二粒子集团理论得到的约化温度值更为精确。二粒子集团理论考虑了近邻分子间的短程关联,由此可知在双轴向列相液晶的研究中考虑近邻分子间的短程关联是非常必要的。

英文摘要：

Based on the model of biaxial nematic liquid crystals, the Landau point in the biaxial nematic liquid crystals was determined by using bifurcation theory and two-particle cluster theory. The molecular biaxial parameter dependent curves transiting from istropic phase to uniaxial nematic phase were obtained. At the Landau point, the results of molecular biaxial parameter λ obtained from bifurcation theory, two-particle cluster theory and mean field theory were the same, but the results of reduced temperature t were different. The reduced temperature obtained from two-particle cluster theory was more accurate. The result of two-particle cluster theory was more reasonable than those obtained from the other two theories. The results demonstrate that it is necessary to consider the short range correlation between each pair of neighbor molecules.