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chuchu6816金虫 (正式写手)
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【讨论】TS 时 出现Wrong number of negative eigenvalues: Desired= 0 Actual=
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在优化过渡态时 有时出现：Optimization stopped. >> -- Wrong number of negative eigenvalues: Desired= 0 Actual 但是加入 noeigen 就会避免这种错误 但是原因是什么啊？在网上搜了一点资料如下。但是看完以后还不怎么了解。希望大家再此讨论一下。 Dear all, Here is a summary of the responses I received regarding my query posted a week ago. Thank you to Patrik Johansson, Stefan Fau, Stephan Graf and Wibke Sudholt for your interest. I was in fact unable to reproduce the error so maybe it was a one off error, albeit a somewhat peculiar one. The problem seems to occur at a change in symmetry of the TS/product. =========> Original Query <========== I have been doing some ab initio calculations recently on the ring opening of cyclobutene using GAUSSIAN94. I have completed an optimisation of the transition state corresponding to the ring opening and formation of the TRANS product (trans-butadiene). To check that the transition state corresponds to the trans conformation an IRC calculation was performed to follow the path in the direction TOWARDS (reverse direction) the trans product. The command line was: >> # RHF/6-31G(d) IRC(CalcFC,Reverse,Stepsize=40,maxpoints=24) The calculation stopped on the 12th point along the path after 5 optimisation steps having failed to converge with this unusual message: >> Optimization stopped. >> -- Wrong number of negative eigenvalues: Desired= 0 Actual=*** This is very peculiar - I have never seen this before. It is highly unlikely that the calculation has 'stumbled upon' another saddle point. Has anyone come across this before? Any reasons/suggestions/ideas would be welcomed. RESPONSES ==========> 1 <========== Hi Dave Your problem sound like one I encountered about a year ago, maybe you've stumbled into a bifurcation point.. If this is the case it would mean that your IRC calc cannot proceed since two alternative ways - truely equal from the calc point of view - are possible, this would for example be possible if the point where your calc crashes has a C2 or Cs symmetry ( or close to ). The way to check and to let the calc. continue is : 1. to perform a freq calc at the IRC point immediately before your calc crashes ( perhaps with a smaller stepsize.) 2. Check the resulting imaginary freqs and see which mode that corresponds to the path you would like to continue along. 3. Move your geometry away from the bifurc point by using the mode above. 4. Perform a new IRC calc from this new geometry. best wishes Patrik ==========> 2 <========== Hi Dave, something went seriously wrong with your IRC. The three stars indicate >999 negative eigenvalues! This is a problem of the actual run and might just vanish on repeating the calculation. By the way, it is advisable to start with the read in structure and hessian matrix of the confirmed TS using IRC(...,readfc,...) and geom=check since this avoids problems due to low numerical accuracy of the input TS structure. If you continue having problems, try to reduce the stepsize and increase the accuracy (using the tight option). Greetings, Stefan ==========> 3 <========== Hi Dave, I had a similar problem during the optimization of saddle points structures. Sometimes G94 stopped with the same message. It seems that there is a bug in the G94 routine which counts the number of negative eigenvalues. Because after testing the structure with a frequency job, I got the correct number of negative eigenvalues. With the OPT keyword is the NoEigenTest option available, which omits the counting of the negative eigenvalues. Unfortunately this option is not listed for the IRC keyword (at least on www.gaussian.com). But ther is maybe an IOp which does the same. Hope this helps, |
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2楼2009-11-24 20:53:29
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