Quantum chemistry-ORCA software package. I performed a geometry scan first :
! PBE0 SVP NumFreq D3 TightSCF
! ScanTS
%geom Scan
B 7 27 = 2.654, 0.9, 40
end
end
----> It performs a surface scan in 40 steps am but not able to locate the transitional state. The coordinates of the step which has the highest energy was taken as the transitional state guess.
! PBE0 SVP OptTS NumFreq
%geom
Calc_Hess true # Calculate Hessian in the beginning
NumHess true # Request numerical Hessian (analytical not available)
Recalc_Hess 5 # Recalculate the Hessian every 5 steps
end
----> I perform OptTS on this coordinates but am not arriving at the transitional state.
I think I made a good guess for the transitional state from the geometry scan .
Can anyone tell me how to find Transitional state in ORCA using ScanTS or OptTS.
Transition state optimization is always tricky irrespective of the software used. If you think you have good guess then try some more times with little modification of input geometry or you can try first optimize at some lower level to get a good guess and hessian.
Transition state optimization is always tricky irrespective of the software used. If you think you have good guess then try some more times with little modification of input geometry or you can try first optimize at some lower level to get a good guess and hessian.
Hello,
What type of reaction are you investigating and what coordinate did you scan (bond length, angle, dihedral)?
What do you mean by you didn't find the transition state? I guess you found either zero or multiple imaginary modes upon calculation of the frequencies after using OptTS in Orca? If you got multiple negative frequencies, was one of them stronger, how much are the other ones?
Maybe you'll need to use quasi-synchronous methods or nudged elastic band, but these are not implemented in orca. I can help and provide a good guess if needed.
Best
Gilles
@ Gilles Berger The reaction am investigating is beta-elimination reaction and the I scanned the coordinates for bond length.
You are right, I got multiple imaginary modes using OptTS. In the first scan I got -247 and -15 while in the next scan it went to -218 and -12 and this continued till it almost reached the ground state.
I am not aware of the methods which you are referring in your reply. I would be really great if you could help me with this and suggest me a method which provides good guess for the transition state.
Thanks in advance
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