How do I identify electronic transitions (sigma to sigma*, pi to pi*, n to sigma* and n to pi*) in experimental UV-Vis spectra of molecules with help of TD-DFT calculations?
TDDFT calculation in gaussian prints the orbital number between which the transition is occurring. You can plot those orbitals in chemcraft and get an idea about the nature of the transition.
For some systems, depending on the code, the program prints out the molecular orbitals symmetry! If Gaussian do not recognized the symmetries for your systems, you should do the "Soumen Ghosh" sugestion! To sign the experimental peaks, you have to compare the energy excitations in your calculation to the experimental data that you have! At Gaussview should have a tool to plot some kind of electronic excitation graphic given your .out or .fchk
hello.... I need to know a similar thing! I can get excitation energy and oscillator strength direct from gaussian03 output. they are giving the orbitals and their coefficient also for each transition. but i want to calculate the %homo-lumo or % MLCT associated to a particular transition, say S0-S1. how to do it? please help. and also tell me how to calculate charge density differnce for a specific transition such as S0-S1?
dear rituparna,
percentage calculation of a particular excitation depends on the nature of the system. If it is a closed shell system then square of the coefficient multiplied by 2*100 is the percentage contribution. But for open shell system you have to normalize the coefficient .In that case square of the coefficient divided by sum of the square of the all coefficient for that excited state multiplied by 100 is the percentage contribution.
It's a closed shell system :) thnks a lot soumen! U mean sq of the coeff multiplied by 200 right?
I suggest to look at a similar question of Soumen Ghosh and answers to it, see the link
https://www.researchgate.net/post/How_to_calculate_percentage_contribution_of_a_particular_excitation_from_TDDFT_output_of_Gaussian09
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