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ldongmei

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[交流] 【求助】关于casscf方法计算激发态的活性空间选择

大家好，casscf方法计算激发态，最重要的是不是活性空间的选择？怎样选？然后又怎样选择调轨道呢？朋友们了解的，都过来说说你们的认识吧，谢谢。

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1楼 2009-12-28 16:48:19

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How to Choose Active Orbitals?
There is no general answer to this question. Attempts have been made
but with rather limited success.
If you have no idea, choose a large active space and run RASSCF(SDTQ...)
with only a small number of orbitals in RAS2.
This has to be done on several points on an energy surface.
Choose as active the orbitals with occupation numbers > 0:02 or < 1:98.
If this is not possible, choose another method.
Use the same active space for the whole surface.

Excited States of Conjugated Organic Moelcules

Use preferably all -orbitals.
Add appropriate lone-pair orbitals.
Add 3s,3p,3d Rydberg orbitals if the spectrum extends into this region.
Note that this requires special basis sets.
Sometimes it is necessary to add extra valence orbitals in order to avoid
intruder states. Alternatively level shift can be used.

Active Spaces in TM compounds
For Mn-Cu use preferably 2 orbitals per doubly occupied 3d orbital (the
double shell eect). These may include ligand orbitals for bond forming
3d orbitals. This is enough for d-d transitions in ionic compounds (10
orbitals).
If CT transitions, corresponding ligand orbital must be included.
Sometimes it is not possible to nd an appropriate active space that is
small enough!
Core correlation and relativistic eects are important already for the rst
row of TM.

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2楼2009-12-28 17:48:02

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