I’m reaching out here because I couldn’t get a clear answer from the developer’s forum.
I’m calculating ESD-associated rates like kF, kP, kISC, and kIC using the adiabatic Hessian model, thoroughly accounting for H-T, Duschinsky rotation, and generally following the suggestions provided in Manual.
Unfortunately, the K*K value is quite large — at least 18 — which prevents the proper application of the output. So far, I’ve tried the following options:
- COORDSYS CART
- IFREQFLAG REMOVE TCUTFREQ 100
- IFREQFLAG REMOVE TCUTFREQ 200
…but without success.
For testing purposes, I set:
- IFREQFLAG REMOVE TCUTFREQ 500
…but the K*K value only dropped by 1 unit.
Initially, I thought the issue might be related to hydrogen atom transfer between two adjacent residues. However, in some cases where the hydrogen is on residue 1 in one state and on residue 2 in the other, the K*K values were small — around 2-3 at most — so that doesn’t seem to be the cause. Moreover, the structure remains nearly the same between the states, with little geometric alteration.
Despite that, using USEB FALSE did not improve the K*K value, nor did setting STEPCONSTR 27 (where 27 is the [Avogadro]-1 index of the hydrogen being swapped).
Any advice or suggestions would be greatly appreciated.
Thanks!
EXAMPLE:
------------------------------------------------------------------------------
ORCA EXCITED STATE DYNAMICS
------------------------------------------------------------------------------
Requested calculation: ...ISC
Coordinate system: ...Deloc. Internal (BAKER)
Lineshape function: ...Gaussian
Excited state PES: ...adiabatic hessian
Apply Duschinsky rotation: ...yes
Use operator derivatives: ...yes
Convert derivatives between states: ...no
Use same frequencies: ...no
Multiroot calculation: ...no
Single mode calculation: ...no
Selected mode calculation: ...no
Initial state hessian: S1.hess
Reading initial state hessian: ...done
Final state hessian: T3.hess
Reading final state hessian: ...done
As a TS Hessian was given, HessFlag is now AH!
Adjusting all geometries to center of mass: ...done
Rotating the excited state geometry: ...done
The RMSD is: 0.085143
Writing FS hessian to: kISC_1.FS.hess
Calculating Wilson’s B Matrix: ...done
Converting to internal coordinates: ...done
Calculating rotation matrix J: ...done
Calculating displacement vector K: ...done
The sum of K*K is: 12.855153
WARNING! Something might be seriously wrong here.
Please check the manual about large values of K*K.