I want to run PES scans on compounds which may proceed photoisomerization, such as C=C/N=N/C=N bond rotations during excited state.
Is the following input file appropriate?
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# TD(NStates=1,singlet,root=1) opt=modredundant B3LYP/6-31+G(d,p) geom=connectivity
coordination coordination coordination
D 1 2 3 4 S 10 18.000000
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10 steps, east step is 18 degree. Suppose I can obtain profile of energy with respect to rotation angle.
The route section is fine. Just a small point you do not need to mention "singlet,root=1" in the route section. These are default options.
18 degree step might be large. You may start with a smaller basis set to decide the appropriate step size. I think 10 degree would be appropriate.
Input looks fine. You can not get a surface, though, just by scanning one coordinate!
I would also suggest you to find out the TS, which you can do using QST2 option and then do the IRC calculation. It will give you the reaction path and the activation energy for the isomerization process, which you can compare with the energy of the light.
For a 180 degrees scan with a step size of 18 degrees, you shall need 9 steps, not 10. However, you should reduce the step size as suggested by Tuhin.
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