外电场作用下MoS2的分子结构和电子光谱

Molecular structure and electronic spectrum of MoS2 under external electric field

各种新型材料改善了人类的生产和生活,二维纳米材料更以其独特的物理化学性质成为了研究的热点.二硫化钼(MoS2)作为过渡金属硫化物的代表,具有优异的机械性能和化学稳定性,为研究其外场效应,本文采用密度泛函理论方法优化了MoS2分子在0-0.1 a.u.(0-5.1423×1010V/m)的静电场中基态几何结构,得到了分子密立根电荷分布、偶极矩和总能量;在此基础上,采用含时密度泛函方法研究了MoS2分子紫外-可见(UV-Vis)吸收光谱在此静电场中的变化.结果显示:分子内电荷分布随着外电场的增强发生了整体转移;伴随着电荷的整体转移,电偶极矩随之增大,而分子总能量随之减小;分子最强UV-Vis吸收峰的波长为483nm、摩尔吸收系数为461 L·mol-1·cm-1伴随着外电场的的逐渐增强,分子激发态的摩尔吸收系数明显增大,UV-Vis光谱吸收峰显著红移,外电场为0.08 a.u.时,其吸收峰基本覆盖了整个可见光波长范围.

A variety of new materials have improved the production and life of human beings.Two-dimensional nano materials have become a research hotspot due to their unique physical and chemical properties.Molybdenum disulfide(MoS2)is representative of transition metal sulfide,with excellent mechanical properties and chemical stability.In order to study the influence of’external electrical field on the molecular structure and spectrum,here in this work,the density functional theory with the hybrid B3 LYP at Def2-TZVP level is employed to calculate the geometrical parameters of the ground state of MoS2 molecule under external electric fields ranging from 0 to 0.1 a.u.(0-5.1423 × 1010V/m).Based on the optimized structures,the time-dependent density functional theory at the same level as the above is adopted to calculate the absorption wavelengths and the molar absorption coefficients for the first ten excited states of MoS2 molecule under external electric fields.The results show that the most strongest absorption band is located at 483 nm with a molar absorption coefficient of461 L·mol-1·cm-1 in the UV-Vis absorption spectrum.The intramolecular charge transfers as a whole with the enhancement of the external electric field.The electric dipole moment increases with the external electric field rising,while the total molecular energy decreases with external electric field increasing.With the enhancement of the external electric field,the absorption peaks show a significant redshift.When the electric field increases to 0.1 a.u.,the redshift is obvious.This can be explained as follows.When the external electric field is weaker,the electron transfer in the molecule is not significant.However,with the augment of the external electric field,the electron transfer in the molecule occurs as a whole.This makes the electron interaction between Mo and S weaker,thus the electron transition is more likely to occur.The energy required for excitation is reduced,and the wavelength of the excited state becomes longer,that is,the absorption peak takes a redshift.With the enhancement of the external electric field,the molar absorption coefficient increases obviously.This is because the overall transfer of the external electric field to the electron makes the electron cloud density of the MoS2 molecule increase and the number of electrons in transition augment.This work provides a theoretical basis for the utilization and improvement of MoS2 photoelectric properties,and also enlightens the application research of other photoelectric materials.