Hi,
I want to calculate Ionization potential (IP) and Electron affinity (EA) for a conjugated molecule using some computational package. Among the two approximations (Vertical/Adiabatic), which one needs to be preferred for these calculations.
Thank You
Hello,
If you want to simulate a fast process, you should calculate the vertical IP.
If the geometry of the nuclei have time to return to the ground state, you should calculate the adiabatic IP. In chemistry adiabatic IP is more relevant to my mind.
Hi,
As Yuriy Demidov says It depends the kind of process you are calculating.
If the geometry of the charged species does not change too much the values of vertical and adiabatic are almost the same. There are great reviews of Ionization Potentials and Electron Affinities. I am going to link one of those. They advised you to use the ADIABATIC approximation if you want to compare your IP/EA with experimental results.
http://pubs.acs.org/doi/abs/10.1021/cr990044u
If you get the adiabatic and vertical energies, you can compute the reorganization energy (how much energy is released as the geometry relaxes from the ground state equilibrium (which is strained in the ionic state) to the ionic state equilibrium).
You can estimate from that the width of the photoelectron spectrum band or even rationalize the vibronic activity observed experimentally.
Marcin
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