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标题: 酶与小分子簇模型使用opt=TS优化时出现的不收敛如何解决？ [打印本页]

作者
Author: sun877469558 时间: 2022-8-3 23:19
标题: 酶与小分子簇模型使用opt=TS优化时出现的不收敛如何解决？
研究体系是一个酶与小分子的团簇模型，除了将边界氢饱和以及边界原子固定后，还将小分子的C-S键固定为1.9埃，但提示收敛失败
Old curvilinear step not converged, using linear step:
SCX= 1.03D-06 DXMaxT= 3.00D-01 SCLim= 1.50D-01 Fact= 1.00D+00
Error imposing constraints

虽然看了尝试了http://sobereva.com/61中的一些方法，诸如（1）SCF=NoVarAcc（2）SCF(novaracc,noincfock) int=acc2e=12（3）降低步数opt=(calcfc,ts,noeigen,maxstep=5)都没有用，google之后发现这个报错通常在QST2中发现，请问这该如何解决？

%mem=32GB
%chk=opt_C_S_1.9A_22_8_3.chk
%nprocshared=64
#p opt=(calcfc,ts,noeigen) freq b3lyp/6-31g(d,p) scrf=(smd,solvent=water) em=gd3

输入文件如下

Title Card Required

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eps=4

C H O N S 0
6-31G**
****

作者
Author: wzkchem5 时间: 2022-8-4 00:11
SMD溶剂模型有一定的数值不稳定性，容易导致不收敛。改成PCM试试

作者
Author: chands 时间: 2022-8-4 10:13
本帖最后由 chands 于 2022-8-4 11:19 编辑

你定义了溶剂和基组了呀，坐标后面为什么还加了eps和基组定义？
结构看得脑阔痛，好像电荷数不对劲

有亚胺结构，溶剂为水，不会水解掉吗？

作者
Author: sun877469558 时间: 2022-8-4 13:17
本帖最后由 sun877469558 于 2022-8-4 14:11 编辑

chands 发表于 2022-8-4 10:13
你定义了溶剂和基组了呀，坐标后面为什么还加了eps和基组定义？
结构看得脑阔痛，好像电荷数不对劲

感谢您的回复，因为是酶与小分子的簇模型，所以使用酶的介电常数=4以消除边界的影响
电荷设置为2，是因为有三个谷氨酸质子化后，硫酸基团带一个负电荷
此外，您说的很对，亚胺结构是不稳定，这个反应的发生是酶促萝卜硫苷水解生成糖和糖苷配基，糖苷配基不稳定发生洛森重排生成萝卜硫素，断裂的键用箭头标出

不知以上我的理解对不对

作者
Author: sun877469558 时间: 2022-8-4 14:18

wzkchem5 发表于 2022-8-4 00:11
SMD溶剂模型有一定的数值不稳定性，容易导致不收敛。改成PCM试试

感谢王老师，我去试一试

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