I am using Gaussian to estimate the ionization potential of a cluster of molecules including 6 molecules of Methanol and 1 molecule of Fluorobenzene, I have optimized the geometry of the neutral cluster and then did a single point energy calculation of the optimized geometry with +1 charge, the difference between energy of the two gives me a rough estimate of the IP, my question is how can we interpret this IP, is it the IP of the whole system or the molecule from which the electron has been removed? also by visualizing the HOMO orbitals in both cases I noticed that the HOMO in neutral case is one of the Pi orbitals of the Fluorobenzene ring while in the ionized case it's the bonding orbital of one of the methanol molecules, not sure how to interpret that?
Tahereh Alavi Hi
I hope you will be fine
I have read your problem, there is two way to find the IP. One is you will perform neutral molecules and visualize the HOMO LUMO energy. A highly occupied orbital shows the maximum energy to donate the electron so HOMO energy is equal to IP similarly LUMO shows maximum energy to accept an electron that is also equal to EA. But in another way, you will perform a neutral molecule and note down the energy of the molecule and again perform that molecule after adding + charge and calculating energy. In the end you can calculate the IP by differentiating energy .
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