含Mn2+化合物优化过程不收敛

吕安琪

各位老师好，本人最近在优化一个含Mn2+的化合物分子，优化结果不收敛，请问应该如何解决，输入文件如下：
%chk=mncl4.chk
%nprocshared=14
%mem=30GB
# b3lyp/cc-pvdz opt

20180829

-2 4
报错信息如下：
Annihilation of the first spin contaminant:
S**2 before annihilation     3.7771,   after     3.7501
Convergence failure -- run terminated.
Error termination via Lnk1e in /gpfs/soft/g09/g09D/l502.exe at Mon Nov  5 20:12:23 2018.
Job cpu time:       0 days  0 hours  4 minutes 46.1 seconds.
File lengths (MBytes):  RWF=     10 Int=      0 D2E=      0 Chk=      1 Scr=      1
谢谢大家！

granvia

Most likely the spin multiplicity is 2. Obviously the complex [MnCl4]2+ has a ligand field of tetrahedral configuration which leads to a splitting of Mn’s d orbtials: a set of triple degenerate orbtials with lower energies and a set of double degenerate ones  lying above. Hence, the five d electrons of Mn fill up the three low-lying orbitals, among which, as a result, two are doubly occupied and one singly occupied. That’s why the spin multiplicity is 2 in stead of 4.

吕安琪

granvia 发表于 2018-11-5 21:24
Most likely the spin multiplicity is 2. Obviously the complex [MnCl4]2+ has a ligand field of tetrah ...

按照同样的方法，自旋多重度改为6时可以正常结束，但是想计算就是 自旋多重度为4时的优化过程
In the same way, when the spin multiplicity is changed to 6, it can be ended normally, but the calculation is to be the optimization process when the spin multiplicity is 4.

sobereva

配合物体系，自旋多重度不为基态的时候比为基态的时候往往更难SCF收敛。怎么解决仔细看
解决SCF不收敛问题的方法
http://sobereva.com/61
要有耐心

PS：cc-pvdz给DFT用不是好的做法
谈谈量子化学中基组的选择
http://sobereva.com/336

一颗赛艇

Mn2+离子，四个Cl-弱场配体，d5高自旋很正常

granvia

一颗赛艇 发表于 2018-11-7 04:51
Mn2+离子，四个Cl-弱场配体，d5高自旋很正常

Yes, you’re right. It should be a high spin compound.