π和σ体系彻底分离的高度定域的键轨道基组的建立  

A Procedure for Constructing a Highly Localized and Symmetrical Bond Orbital Basis Set

作　　者：虞忠衡[1] 彭晓琦[1] 郭彦伸[1] 宣正乾[1] 

机构地区：[1]中国科学院化学研究所分子动态和稳态结构国家重点实验室,北京100080

出　　处：《化学学报》2001年第2期179-184,共6页Acta Chimica Sinica

基　　金：国家自然科学基金 ( 2 9872 0 42 ;2 0 0 72 0 41;39890 390 );中国科学院院长特别基金;国家重点基础研究发展规划项目 (G19980 10 10 0 )资助课题

摘　　要：高度定域的、对称的、键轨道基组的建立是一个多步的计算程序 :( 1)以定域片断轨道 [k,i,j]为基 ,对分子作有条件的RHF运算 ,算得FUL和DSIo 态的片断分子轨道 [Фol′,Фon,Фom]和 [Фl,Фn,Фm].在基组 [k,i,j]中 ,i∈双占据和空σ片断分子轨道 (FMOs)组 ,j∈πFMO组 ,k∈单占据σFMO组 ,它们都精确地定域在各自的片断内 ;( 2 )利用Φol′与Φl 间的重叠积分值 (Sl′l>0 .5 ) ,可以从DSIo 态中 ,自动地选出Ns 个对称的、由单占据轨道线性组合而成的分子轨道ol′= akl′k(k =1,2 ,… ,Ns) .接着 ,用Φol′取代FUL态中同类的、非对称轨道组Φl= aklk(k =1,2 ,… ,Ns) ;( 3 )以上述新的轨道组 [Φol′,Φn,Φm]为基 (其中 ,Φol′∈DSIo 态 ,它们离域于整个分子 ;双占据及空σFMO组Φn和πFMO组Φm 属于FUL态 ) ,按FUL态的条件 ,再次对分子作有条件的RHF运算 ,从中得到一组对称的、闭壳层正则FMOs,而且每一个FMO均有正确的电子占据数 ;( 4)利用Perkin原理 ,将第 3步所得的正则FMO组定域成一个对称的键轨道基组 [Φl′,Φn′,Φm′].在这个基组中 ,π体系Φm′与σ构架Φn′是彻底分离的 。A procedure for constructing a highly localized and symmetrical bond orbital basis set with the π systems separated off from the σ frameworks has been developed. It is a four-step procedure: (1)over the opened-shell localized fragment molecular orbital (FMO) basis set [_k,_i,_j] where _i∈doubly occ. and vacant σFMOs, _j∈πFMOs, and _k∈singly occ. FMOs, the conditional RHF computations provide each of the FUL and DSI o electronic states of a molecule, such as norbornadiene with a set of the closed-shell FMOs; (2)the symmetrical MOs,  o_ l′=a_ kl′_k (k=1,2,...,N_s) which have delocalized over the whole molecule, in the DSI o substitutes for the unsymmetrical Φ_l=a_ kl_k in FUL state, and those together with other two groups of the unsymmetrical FMOs, Φ_m=a_ jm_j and Φ_n=a_ in_i in the FUL state formed a closed-shell FMO basis set [Φ_n, Φ_m, Φ o_ l′] in which each of FMOs Φ_n and Φ_m is still localized on its corresponding fragment; (3)based on the basis set [Φ_n, Φ_m, Φ o_ l′], the conditional RHF computation for molecule is performed under the following constraint: all F_ ij=0.0 and S_ ij=0.0(i≠j,i∈fragment P, j∈fragment Q, and P≠Q) except for those between Φ o_ l′. It provides a molecule, such as norbornadiene, with a highly localized and symmetrical FMO basis set [Φ_ n′, Φ_ m′,Φ_ l′]; (4)each of the FMOs Φ_ n′, Φ_ m′ and Φ_ l′ is concentrated on a specific atom or two neighboring atoms using the Perkin procedure at last, and it has correct orbital occupancy.

关 键 词：定域轨道基组 片断轨道 微扰分子轨道理论 轨道定域化 键轨道基组 

分 类 号：O641[理学—物理化学]