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[交流] 自旋污染求助

最近做的一个体系自旋污染大的惊人，请教高手
输入：# b3lyp/6-311+g(2d,p) pop=NBO scf=(maxcycle=500, tight)
Charge =  0 Multiplicity = 2

输出：
SCF Done:  E(UB+HF-LYP) =  -5204.25052453    A.U. after 32 cycles
         Convg  = 0.6735D-08          -V/T =  2.0016
         S**2 = 1.9323
Annihilation of the first spin contaminant:
S**2 before annihilation    1.9323, after    2.5168

高斯公司回信：I agree that this is a large value for S**2 but this really is a
statement about system rather than something you can control.

1) have you check the stability of the wavefunction?  You have a number
   of negative eigenvalues, run STABLE=Opt Guess=Read

2) are you sure that a doublet is the lowest energy state, a large
   value for S**2 says the alpha and beta orbitals are different,
   this can occur if you have the highest beta occupied different
   from the alpha orbitals where it may be unoccupied.  Again stability
   may switch this or higher spin states may be more stable.

Try both of these.

可我做了STABLE=Opt 后发现波函数是稳定的
Eigenvectors of the stability matrix:

Eigenvector 1: ?Spin  -A' Eigenvalue= 0.0295043
111A ->112A       0.93202
110B ->111B    -0.18620
110B ->113B    -0.10726
The wavefunction is stable under the perturbations considered.
The wavefunction is already stable.
The wavefunction is already stable.

而且我也作了四重态，发现二重态比四重态的能量低，现在不知道该怎么办了，还请高手指点，　谢谢！

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