I have done some Transition state calculations on UB3LYP/cc-pVTZ level of theory and verified from IRC calculations too. Now i am trying same transition states calculations on CBS-QB3 level of theory but getting an error every time. Any suggestions to overcome this problem ?
CBS-QB3 is a composite method of calculation. Please upload the error files. Then it will be easy to suggest.
Thank you Debasish. Here is the out-put file section......
Item Value Threshold Converged?
Maximum Force 0.005724 0.000450 NO
RMS Force 0.001543 0.000300 NO
Maximum Displacement 0.576824 0.001800 NO
RMS Displacement 0.181808 0.001200 NO
Predicted change in Energy=-3.153493D-04
In the end of output file
Error termination request processed by link 9999.
How to avoid this error termination ?
Probably TS is not converging within default step number. If I remember correctly 1st step of CBS-QB3 is B3LYP/CBSB7 optimization. CBSB7 basis is equivalent to B3LYP/6-311G(2d,d,p). So, you can optimize your TS in this level first and then run CBSQB3 calculation with the final geometry
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