中文摘要：

采用密度泛函理论对Li以不同覆盖度吸附在石墨烯表面上时系统的结构稳定性和场发射性能进行了计算.计算结果表明：Li吸附在石墨烯表面的碳六元环的中心位置时系统的能量最低,随着Li的覆盖度增加,碱金属与石墨烯之间的吸附作用逐渐减弱.在（4×4）R0°结构中,由于碱金属Li的修饰作用,Li/石墨烯体系的功函由原来的4.625eV降至3.156eV,但是随Li的覆盖度增大,系统的功函反而上升.电荷分布和态密度结果表明：随Li覆盖度增大,碱金属Li—Li之间的排斥作用逐渐增强,这不仅导致金属向石墨烯转移电子数逐渐减少,同时还使得Li层的功函较纯Li金属表面功函明显增加,这是Li/石墨烯的功函不会因Li覆盖度增加而单调递减的原因.

英文摘要：

Relying on the density functional theory（DFT）,the structural stability and field emission performance of Li/graphene compound with different Li coverage were investigated.The results indicated that the adsorption of single Li atom on the center site of hexatomic ring is energetically favorable.With the increase of Li coverage,the adsorption interaction between Li and graphene are gradually weakened.Due to the modification effect of Li,the work function of（4×4）R0°Li/graphene structure decreases from 4.625 to 3.156 eV,but the work function anomalously increases with increasing Li coverage.Owing to the strengthened repulsion effect between Li atoms,the density of states and Mulliken charges suggested that the transferred electrons from Li to graphene gradually decreases.Meanwhile,the work functions of Li layers obviously enhance in comparison to that of the Li metal surface.These factors mentioned above mainly cause the work function variation trend of Li/graphene with different Li coverage.