Phosphorescence lifetime formula used in dalton.

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lopa
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Phosphorescence lifetime formula used in dalton.

Post by lopa » 28 Apr 2016, 20:20

Hello!
I calculated phosphorescence lifetime using dalton, but it is giving much larger lifetime than what obtained experimentally.
If anyone could provide the formula used for phosphorescence lifetime calculation in dalton, it will be a great help.

Thank you...

taylor
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Re: Phosphorescence lifetime formula used in dalton.

Post by taylor » 28 Apr 2016, 22:13

And you would be calculating the phosphorescence of...? DNA? The 2D state of nitrogen atom in the aurora borealis? And you are using what method? And what basis set?

I think the lesser question is "what formula is used in Dalton" (you have the source, to start with, and the program is pretty good about listing conversion factors) and more what you are trying to actually do. If you tell us that, we may be able to help...

Best regards
Pete

sonco
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Re: Phosphorescence lifetime formula used in dalton.

Post by sonco » 29 Apr 2016, 08:02

In the dalton manual, at the beginning of the section describing the keywords for phosphorescence (Quadratic Response section)
there is a list of references.
Check those dealing with triplet quadratic response.

Sonia

sonco
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Re: Phosphorescence lifetime formula used in dalton.

Post by sonco » 29 Apr 2016, 08:07

Pete is of course 100% right, most important is the choice of basis/method for the system you want to treat. But it's always good to make sure the formula is used is the one
one wanted to use :-)

--
Sonia

Bernd S.
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Re: Phosphorescence lifetime formula used in dalton.

Post by Bernd S. » 29 Apr 2016, 14:28

Well, I would be more worried if the calculated lifetime was much shorter than the measured one. Perhaps you should think about some competing relaxation pathes. For example, lifetimes may depend drastically on a solvent and changing from H2O to D2O can increase the lifetime by orders of magnitude.

lopa
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Re: Phosphorescence lifetime formula used in dalton.

Post by lopa » 01 May 2016, 06:30

Hello!
Firstly, I apologize for being too short in my approach. To be a bit elaborate, I'm working on a stacked organic molecule (dimer). I've optimized the structure using gaussian 09, and used its optimized co-ordinate to calculate the phosphorescence lifetime using dalton. I've used cam-b3lyp and cc-pVDZ as the functional and basis-set respectively. The life-time thus obtained is much larger than the experimental observation.

The part of the lifetime is as follows:
Phosphorescence transition rate from excited state no. 1
(Triplet->singlet transition, high-temperature limit)


Transition energy: 2.697 eV

Partial rates (ECSO): X-polarization 5.39964E-02 Transition moment : 5.090E-05
Partial rates (ECSO): Y-polarization 1.87561E-04 Transition moment : 3.000E-06
Partial rates (ECSO): Z-polarization 3.03834E-03 Transition moment : 1.207E-05

Oscillator strength (ECSO) 1.814E-10
Total transition rate (ECSO) 1.907E-02 s-1
Total phosphorescence lifetime (ECSO) 5.243E+01 s


Whereas, reported experimental lifetime is only 1.07 seconds.
I'm not using any solvent, so solvent effect has no role to affect the lifetime.

The obtained lifetime is much larger, and I've also noticed a few posts in the forum claiming larger phosphorescence lifetime obtained.
I've attached the out file for convenience (the dal and mol file are present in out file).
If anyone could explain the reason for the large lifetime obtained, it would be a great help.

Thank you...
Attachments
DPhCzT-stacked-t1-tdopt.rar
(155.3 KiB) Downloaded 354 times

taylor
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Re: Phosphorescence lifetime formula used in dalton.

Post by taylor » 01 May 2016, 07:02

Please do not post archives: it's very inconvenient. All you need to do is post an (or perhaps if there are multiple issues several) output files. Note that I have not downloaded your post and thus still have no idea what you are doing. Meanwhile...
If anyone could explain the reason for the large lifetime obtained, it would be a great help.
In no particular order: your system may not be well-suited to the many-electron treatment, DFT; even if it is the functional chosen may not be appropriate; the basis set might not be appropriate/adequate; there may be environmental factors as Bernd posted a couple of days ago.

There does seem to be a degree of misunderstanding here. The program is (to the best of our debugging abilities) correct, in that the answer you get at a given computational level with a given basis for a given property is the right answer at that level of treatment. This has nothing to do with whether it is "correct" in the sense of agreeing with experiment! In the case that the computational method is full CI in an infinite basis, we would obtain the exact solution to the nonrelativistic Schroedinger equation, but that still might not agree with experiment because of environmental or finite-temperature effects. You are comparing apples to oranges. And the experimentalists are probably not measuring a lifetime, they are most likely extracting a "lifetime" from other measured quantities.

All is not lost here. What I would suggest is that you find a small system that is representative of the important structural features of your target molecule. For example, if the chromophore is a CO group, you could try methanal or acetone, or if it's a conjugated system butadiene, or if it's a conjugated system with a CO chromophore acrolein, etc. With a small representative system you can then try (and try quickly because the calculations will be relatively fast) a variety of different methods, including elaborate treatments like CC3. By trying a small system and comparing results to experiment you should get an idea of which methods might be suitable for your "real" molecule. There are still uncertainties: even if you get good agreement between the phosphorescence lifetime for methanal lowest triplet state and a gas-phase experiment with method A and basis set B this does not guarantee method A/basis B will be appropriate for your "real" molecule, but we can be pretty damn sure of the converse! If method A/basis B does not work for say methanal the odds are very heavily against it working for anything else.

Best regards
Pete
P.S. (Full disclaimer: I wrote it) if you can find a copy of the lecture notes for the European Summerschool in Quantum Chemistry (published originally by Springer and republished every two years for each school) there is an article on "Accurate Calculations and Calibration" that discusses a lot of these issues about design of calculations. It was written many years ago and has not been updated but I think the general principles are still sound. If you cannot find it, let me know and I can probably find a version of it to send you, but I would have to search around a bit on our home cluster and this is not convenient right now.

lopa
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Re: Phosphorescence lifetime formula used in dalton.

Post by lopa » 01 May 2016, 07:24

Dear Taylor
Firstly, sorry for the inconvenience from my part, and secondly thank you very much for your suggestions, I'll try to do so.
Thank you.

Bernd S.
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Re: Phosphorescence lifetime formula used in dalton.

Post by Bernd S. » 01 May 2016, 09:57

A factor of 50 in the lifetimes doesn't sound to me like a major headache. In my humble opinion it makes much more sense to look at a sequence of compounds with, e.g. , substituting along the series of halides and looking at that effect with experiment as well. I most likely should never apply for a job in advertisement, but quantum chemistry is not always a tool for looking at absolute numbers but rather at trends and understanding them in a more simple lay men's language like HOMO LUMO gap, population abalysis or whatever you prefer. I don't earn a dime on it so I can honestly support the suggestion to read Pete's sections in the ESC summer school books. "When I find myself in times of trouble
Father Pete just comes to me. Speaking words of wisdom Let it be .." ;-)

taylor
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Re: Phosphorescence lifetime formula used in dalton.

Post by taylor » 01 May 2016, 17:58

Bernd, have to admit I like it!

Best regards
Pete

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