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 ,而且这两个轨道组始终精确地定域在各自的片断内 The highly localized, symmetric, key orbital basis set is a multi-step computational procedure: (1) conditional on the molecular basis of the localized fragment orbit [k, i, j] , The molecular orbitals [Фol ’, Фon, Фom] and [Фl, Фn, Фm] of the fragment in the FUL and DSIo states are computed, and 基i ∈ double occupancy and empty in the basis set [k, i, j] σMO group, j∈πFMO group, k∈single-occupy σFMO group, all of them are precisely localized in their respective fragments. (2) By using the overlap integral value between Φol ’andΦl ’L> 0 .5), from the DSIo state, Ns can be automatically selected from the linear combination of single occupied orbit molecular trajectory  ol’ = akl’k (k = 1,2, ... , Ns). Then, the same symmetric orbit group Φl = aklk (k = 1,2, ..., Ns) in the FUL state is replaced by Φol; (3) Φn, Φm] (where Φol’∈DSIo states, which are off-domains in the whole molecule; the Φn and πFMO groups of the double-occupying and empty σFMO groups Φm belong to the FUL state), and according to the condition of FUL, The RHF operation, from which a group of symmetric, closed shell positive FMOs, and each FMO has the correct electronic occupancy. (4) Using the Perkin principle, the regular FMO group obtained in Step 3 is localized into a symmetric key orbit basis set [Φl ’, Φn’, ​​Φm ’] In this basis set, the π system Φm ’and the σ frame Φn’ are completely separated, and the two track sets are always precisely located within the respective segments