苯环活性空间的选取

xujian

PhOO自由基的计算文献中( JPCA, 2000, 104, 3004)，做CASSCF计算时，选择了7个电子8个轨道（CASSCF(7，8)）,请问苯环的活性电子和轨道取得是多少，分别是哪些轨道，谢谢!

sobereva

原文不是写了么
The active space for the CASSCF calculations was problematic to
determine for the disparate structures, as most of them were of
C1 symmetry. For 1 (Cs symmetry), six orbitals were of ð symmetry,
and the two chosen ó orbitals had large O-O interactions.
For the other structures, the four highest occupied and
four lowest unoccupied orbitals were used as obtained from
ROHF/6-31G* wave functions.

这里CASSCF是基于MO做的，涉及的轨道是对整体而言的，不是对某个局部片段而言的

xujian

sobereva 发表于 2017-4-6 15:05
原文不是写了么
The active space for the CASSCF calculations was problematic to
determine for the d ...

sob老师，做cas计算时，轨道要成对选，而文献（molecular physics, 2003, 101, 2103）中写道For benzene a full valence pi active space comprises 6 electrons in 6 orbitals (CAS (6/6)), 为什么pi*不用选在里面？

pwzhou

xujian 发表于 2017-4-6 15:41
sob老师，做cas计算时，轨道要成对选，而文献（molecular physics, 2003, 101, 2103）中写道For benzene  ...

(6,6)不就是3个pi轨道加上3个pi*轨道吗？

xujian

pwzhou 发表于 2017-4-6 15:55
(6,6)不就是3个pi轨道加上3个pi*轨道吗？

对的，我搞笑了，文献中“For monohalobenzenes an active space was employed which includes the x-orbitals from the benzene ring (6 pi, CAS (6/6)) and the chlorine or bromine atom (2 pi, CAS (8/8)), as well as the bonding orbital between carbon and the halogen (2 sigma, CAS (lO/lO), and the corresponding anti-bonding orbitals.”为什么卤素与C之间要考虑pi键

pwzhou

xujian 发表于 2017-4-6 16:23
对的，我搞笑了，文献中“For monohalobenzenes an active space was employed which includes t ...

活化空间的选择和体系以及研究的问题密切相关，怎么样选择活化空间不是简单一两句话就能说清楚的，建议你好好看看相关文献。

xujian

pwzhou 发表于 2017-4-7 08:31
活化空间的选择和体系以及研究的问题密切相关，怎么样选择活化空间不是简单一两句话就能说清楚的，建议你 ...

谢谢！我理解是Cl或者Br两个p轨道上的电子与苯环形成pi键，不知道是否正确，但如果这样的话为何不用考虑pi反键呢？文献说苯胺中“the long pair orbital from the nitrogen (2l, CAS(8,8))”N原子上的孤对电子怎么会占据两个轨道，麻烦您！