Method for studying intramolecular charge transfer

moiumuio

Hi everyone,
I am using FMO isosurface analysis to figure out the intramolecular charge transfer (ICT) effect of a cyanide anion probe, just like in the piece I have attached. We can see the FMO isosurface study of the complex when the cyanide anion binds to the probe in the attached figure (the probe is on top, and probe-CN is below, the iodine anion was simplified). Can I claim that the ICT effect did not happen in the complex based on these analyses, or do I need a better one?
Thank you.

sobereva

Using FMO to analyze this problem is never recommended, because much more orbitals may be involved in charge transfer.
The best way is plotting electron density map using Multiwfn (http://sobereva.com/multiwfn) to visually characterize the charge transfer, see Section 4.5.5 of Multiwfn manual for example, and calculate fragment charge to quantify the amount of charge transfer (In main function 7 of multiwfn, using option -1 to define a fragment first, and then choose one of methods to calculate atomic charges, then fragment charge will be outputted together).

moiumuio

sobereva 发表于 2024-5-1 10:19
Using FMO to analyze this problem is never recommended, because much more orbitals may be involved i ...

Greetings, prof.
Does measuring the amount of charge transfer for fragment charge require me to perform TDDFT? My issue stems from the fact that the solvent I utilized was a DMSO and water blend. So, I have to perform TDDFT for every solvent?

sobereva

moiumuio 发表于 2024-5-1 12:04
Greetings, prof.
Does measuring the amount of charge transfer for fragment charge require me to p ...

This depends on the mechanism causing charge transfer. If the charge transfer is caused by electronic excitation, evidently you must perform electron excitation via e.g. TDDFT, so that you can calculate fragment charge based on excited state density.
In Gaussian, you can define a mixed solvent, the way has been described in http://sobereva.com/327.

moiumuio

sobereva 2024-5-1 22:46
This depends on the mechanism causing charge transfer. If the charge transfer is caused by electro ...

Thank you, professor.
My GS structure was optimised for wB97XD and ma-def2-SVP. Do I have to change the basis set to ma-def2-TZVP for SP and TDDFT calculations?
And do I use IFCT to measure the amount of charge transfer or do I still need to calculate fragment charge?

sobereva

moiumuio 发表于 2024-5-1 23:31
sobereva 2024-5-1 22:46
This depends on the mechanism causing charge transfer. If the charge transf ...

If changing to ma-def2-TZVP, the result is expected to be better.

No. For quantitatively evaluating charge transfer caused by electronic excitation at TDDFT level, IFCT directly gives what you need.

moiumuio

sobereva 发表于 2024-5-1 22:46
This depends on the mechanism causing charge transfer. If the charge transfer is caused by electro ...

Do I need to use solvent while optimize the GS structure? will solvent effect the GS structure due to the existence of cation?

sobereva

moiumuio 发表于 2024-5-2 20:41
Do I need to use solvent while optimize the GS structure? will solvent effect the GS structure due ...

If the molecule exists in solvent environment, optimizing it with solvation model is the safest way. Implicit solvation model doesn't increase cost notably.

moiumuio

sobereva 发表于 2024-5-2 23:56
If the molecule exists in solvent environment, optimizing it with solvation model is the safest wa ...

Greeting Prof.,
Do I have to include the iodine anion when calculating? And will the absence of iodine affect the result of IFCT?
If I don't need to add the iodine anion to the structure, what is a good explanation for it in the article?
Thank you.

sobereva

moiumuio 发表于 2024-5-5 00:39
Greeting Prof.,
Do I have to include the iodine anion when calculating? And will the absence of i ...

I didn't see the exact position of the iodine anion in your structure, and thus I am unable to give you a definitive answer

moiumuio

sobereva 发表于 2024-5-5 23:48
I didn't see the exact position of the iodine anion in your structure, and thus I am unable to giv ...

I have attached my structure optimized with the iodine anion.
Actually, I decided to eliminate the iodine anion from my structure due to these 2 threads: "http://bbs.keinsci.com/forum.php?mod=viewthread&tid=44811&fromuid=59193" and "http://bbs.keinsci.com/forum.php?mod=viewthread&tid=43381&fromuid=59193".
I just don't know how to explain in text :(

sobereva

moiumuio 发表于 2024-5-6 11:47
I have attached my structure optimized with the iodine anion.
Actually, I decided to eliminate th ...

If in the actual environment (e.g. aqueous environment), iodine anion can easily dissociate from the cation, then it is very reasonable to only calculate the cation part.

moiumuio

sobereva 发表于 2024-5-1 10:19
Using FMO to analyze this problem is never recommended, because much more orbitals may be involved i ...

Greeting prof.
When I calculate the CT% (for 2 fragments) before and after added my quencher, the CT% change from 16% to -0.4%. Can I conclude that my structure has ICT characteristic and that has been quenched by analyte?
Thank you.

sobereva

moiumuio 发表于 2024-6-24 23:31
Greeting prof.
When I calculate the CT% (for 2 fragments) before and after added my quencher, the ...

Please do not simply check CT%, but also visually check hole and electron distributions, otherwise one cannot draw definitive conclusion.

moiumuio

sobereva 发表于 2024-6-25 01:46
Please do not simply check CT%, but also visually check hole and electron distributions, otherwise ...

Hi prof.
I have taken your advice and checked hole and electron distribution. My structure has first excited state, which is dark state with f = 0.095, and second excited state, which is the first bright state with f = 0.981. If I calculate fragment charge and visualize electron and hole distribution based on the first excited state, will the result be meaningful?
Thank you.