Hi,
i have made hydrolysis of peptide from small protein to learn Computational Chemistry basics. While i try to find Transition state of hydrolysis, i saw double imaginary frequency but one of them is -606 A other one is -13. I have tried multiple alternatives but still results was similar. How is it possible? I expect just one of them.
Please check the previous discussions on related topic which may provide the solutions:
https://www.researchgate.net/post/Transition_state-imaginary_frequency-QST32
https://www.researchgate.net/post/What_does_imaginary_frequency_mean_while_optimizing_dimer_geometry_by_DFT_approach/1
1) Check that any of them corresponds to vibration you want to see.
2) 13 cm-1 is most likely artifact, that can be eliminated by reoptimisation of TS with tighter grid and bigger basis set.
That happens often and the second imaginary freq means that you're very close to your transition state, but not exactly there. Try reoptimizing, possibly with different options (tighter grid, scf=qc, opt=z-matrix or opt=cartesian).
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