中文摘要：

采用密度泛函理论（DFT）方法系统研究了碱金属Li原子吸附亚苯基-1,2-亚乙烯基（Phenylenevinylene）聚合物（PPV）及其衍生物（具有给受体基团修饰的）体系的结构和非线性光学性质.Li原子能稳定地吸附在PPV及其衍生物的表面,吸附能高达62.3~78.2 kJ/mol.当碱金属Li原子吸附在[PPV]n（n=2~4）表面时,锂盐效应导致了Li原子和[PPV]n之间发生了明显的电荷转移过程,使体系的一阶超极化率β0从249~756 a.u.明显增加到1.16×104~1.37×105a.u..当碱金属Li原子吸附在只有给体（—NH2）或只有受体（—CN）基团修饰的PPV衍生物{[NH2-（PPV）n]/[（PPV）n-CN]}时,体系的一阶超极化率值进一步提升,分别高达1.61×105a.u.（n=4）和2.85×105a.u.（n=4）.这主要源于锂盐效应和Donor-π-Acceptor之间的协同作用导致跃迁能进一步降低所致.在Li原子吸附的具有给受体基团同时修饰的PPV衍生物（Li@[NH2-（PPV）n-CN]）体系中,这种协同作用得到进一步加强,显著改善了体系的一阶超极化率（高达3.56×105a.u.,n=4）.

英文摘要：

By means of the density functional theory（DFT） method, we investigated detailedly the structures and nonlinear optical（NLO） properties of the adsorbed phenylenevinylene （PPV） polymer with the alkali metal Li atom and its corresponding derivatives systems decorated with the donor/acceptor group. In these PPV- based systems, the Li atom can be adsorbed stably on the surfaces of PPV and its derivatives, as revealed by their considerable adsorption energies （62. 3--78.2 kJ/mol）. It is revealed that when adsorbing the Li atom on the [ PPV ] ,（ n = 2--4 ）, the evident charge transfer can occur between them, and this effect of lithium salt can effectively enhance the first hyperpolarizabilities β0 values of PPV systems from original 249--756 a.u. to the range of 1.16×104--1.37×105 a.u. Comparatively, when adsorbing the alkali metal Li atom on the PPV derivatives modified with only donor（--NHz） or acceptor（--CN） group, the first hyperpolarizabilities of sys- tems can be significantly improved further, where the β0 values of Li@ [ NHz-（PPV）4 ] and Li@ [ （PPV）4- CN] can be as large as 1.61×105 and 2. 85×105 a. u. , respectively. This can be attributed to the case that the cooperation effect of lithium salt and Donor-π-Acceptor can result in the more evident decrease of main transition energy of system. Further, this cooperation effect can be strengthened significantly in the Li-ad- sorbed PPV derivatives decorated with donor/acceptor（-NH2/-CN） pairs, which can lead to the more effective improvement ofβ0 value（ up to 3.56×105 a. u. at n=4）. This work can provide some new valuable in- sights for designing the new type of high-performance NLO materials based on the excellent PPV systems.