中文摘要：

采用平面波赝势方法（PAW）和局域密度近似（LDA）的第一性原理方法计算了双甲基脲晶体的电子结构,采用密度矩阵理论计算了双甲基脲晶体的介电函数和倍频系数,并将二阶非线性光学系数谱的特征峰与介电函数光谱结合起来,按单、双光子共振项进行分析。与尿素晶体的光学性质比较分析表明：双甲基脲晶体的线性与非线性光学性质与尿素相似,并且双甲基脲晶体中的甲基对其二阶谐波产生通过虚空穴过程产生了积极的影响。

英文摘要：

A first-principles study of the dielectric functions and the second-order optical response functions of N,N＇-dimethylurea（DMU） crystal was performed.The highly accurate full-potential projected augmented wave（PAW） method was used in the calculation of the electronic structure of DMU crystal.The microscopic mechanism of the linear and nonlinear optical properties of DMU crystal has been analyzed by coupling optical spectrum and the electronic structure.The optical and nonlinear optical properties of DMU crystal are similar to those of urea crystal,and the contribution of substitutional group（CH3） to the SHG effect is due to the virtual hole（VH） process for DMU crystal.