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aerospace

Member

Registered: 2021-08-17

Posts: 3

Calculating the excited state dipole moment

Dear Mr. Lu,

I am trying to calculate the dipole moment of an excited state, using "Gaussian" software. My input commands were: "opt freq td=(singlets,nstates=5,root=1) cam-b3lyp/6-31g(d) geom=connectivity" as I wanted to optimize the geometry of S1 state (starting from optimized S0 structure) and calculate the S1 dipole moment of the optimized structure. I am wondering, is this is the correct way to do the excited state dipole moment calculation? Moreover, is the Dipole moment in an output after the last "Population analysis using the SCF Density" the correct dipole moment of the excited state? I have looked for the answers over the Internet, however, information regarding this issue is very limited.

Thank you very much in advance for your help!

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: Calculating the excited state dipole moment

Usually you need two steps:

(1) Optimize S1: # opt td cam-b3lyp/6-31g(d)   PS: "singlest" and "root=1" are default options, so they are not specified explicitly. Since only S1 is of interest, the default nstates=3 is enough. You can also add "freq" if you want to check if there are imaginary frequencies

(2) Calculate dipole moment for S1: Use geometry of last step and use keywords: # td cam-b3lyp/6-31g(d) density. Then the outputted dipole moment is that of S1 corresponding to relaxed density. Note that "density" must be added, otherwise population analysis will be conducted for ground state wavefunction and thus you will obtain ground state dipole moment at S1 geometry.

BTW: There is also another type of excited state dipole moment, which corresponds to unrelaxed excited state density. To calculate it, you can directly use Multiwfn, see Section 3.21.5 of Multiwfn manual.

aerospace

Member

Registered: 2021-08-17

Posts: 3

Re: Calculating the excited state dipole moment

Thank you very much for the answer! I have read the "Exploring Chemistry with Electronic Structure Methods", however, this procedure was not explicitly stated there, so I had some doubts. Therefore, I am really grateful for your insights.