Hi Michael,

it looks like this is not only a how-to issue on selecting methods (us= ual disclaimer: what I say may be wrong.) It would definitely be useful to = make sure you are using the right theoretical framework altogether. This in= turn will allow you to choose test cases, simpler calculations for comparison, etc.

Great to see the old CCL magic working well 25 years on; a tribute to = Jan Labanowski and the community. It is one of the best online communities = I have observed since Jan brought 100 of us together after a conference to = start the list. This exchange proves it yet again. Kudos all!

Yours,

Alejandro Pisanty

- - - - - - - - - - - - - - - - - - - - - - - - - - -
Dr. Alejandro Pisanty
Facultad de Qu=EDmica UNAM

Av. Universidad 3000, 04510 Mexico DF Mexico

<= /div>

+52-1-554144447= 5 FROM ABROAD

+525541444475 DESDE M=C9XICO SMS +525541444475
Blog: http://pisanty.blogspot.com
LinkedIn: http://www.linkedin.com/in/pisanty
Unete al grupo UNAM en LinkedIn, http://www.linkedin.com/e/gis/22285/4A106C= 0C8614
Twitter: http://twitter.com/apisanty
---->> Unete a ISOC Mexico, http://www.isoc.org
. . . . . . . . . .&n= bsp; . . . . . .

Desde: owner-chemistry+apisan=3D=3Dse= rvidor.unam.mx-x-ccl.net [owner-chemistry+apisan=3D=3Dservidor.unam.mx-x-cc= l.net] en nombre de Michael Morgan michaelmorgan937,,gmail.com [owner-chemistry-x-ccl.net]
Enviado el: mi=E9rcoles, 17 de agosto de 2016 11:14
Hasta: Dr. Alejandro Pisanty Baruch
Asunto: CCL:G: triplet TDDFT calculation

Dear Per-Ola,

Thank you very much fo= r your kind input!

Now I remember Gaussia= n manual states the TDDFT calculations are only effective for close shell s= ystems. Probably I need look at other methods as you suggested CASPT2.

Thank you.

Best regards,

Michael

From: owner-chemistry+michaelmorgan937=3D= =3Dgmail.com() ccl.net [mailto:owner-chemistry+michaelmorgan937=3D=3Dgm= ail.com() ccl.net] On Behalf Of Norrby, Per-Ola Per-Ola.Norrby^^astrazeneca.com
Sent: Wednesday, August 17, 2016 1:48 AM
To: Morgan, Michael <michaelmorgan937() gmail.com>
Subject: CCL:G: triplet TDDFT calculation

Dear Michael,

You get variable <S= **2> because you use the unrestricted approximation. For a triplet, the = exact value of <S**2> is 2; any value higher than that indicates cont= amination from higher states. There is no easy or cheap way out of this. You could use restricted open shell calculations, R= O instead of the default U (not sure about Gaussian, I=92ve done those in J= aguar), but in my experience, energies are less reliable even though you=92= re guaranteed pure spin states. For ground state calculations, you can project out most of the higher spins in= the unrestricted solution, but again, I=92m not sure the method is availab= le for TDDFT. For accurate identification of =93real=94 excited states, I= =92ve used CASSCF/CASPT2, but even there, the energies from unrestricted TDDFT can be as good or better. I did find = the CASPT2 calculations good for evaluating which of the DFT excited states= were =93real=94, and which were artifacts in the unrestricted approximatio= n. Not published, just experience from a long project we never managed to finalize.

Best regards,

Per-Ola

From: owner-chemistry+per-ola.norrby=3D= =3Dastrazeneca.com=CCl.net [mailto:owner-chemistry+per-ola.norrby=3D=3D= astrazeneca.com=CCl.net] On Behalf Of Michael Morgan michaelmorgan937%gmail.com
Sent: den 17 augusti 2016 05:42
To: Norrby, Per-Ola <Per-Ola.Norrby=3Dtrazeneca.com>
Subject: CCL:G: triplet TDDFT calculation

Dear All,

Standard TDDFT calculations calculate singlet->si= nglet excitations. In Gaussian, I can see that for each excitation, <S**= 2>=3D0.000.

While I calculate molecules like O2 which the ground= state is triplet, I need calculate triplet->triplet excitations by assi= gning TD=3Dtriplet .
In output, I found all kinds of <S**2> values (from 2 to 4). I am con= fused: for those are not close to 3, are they still spin-allowed therefore
experimentally observable? Should I include them if I want to predict an ab= sorption spectrum for the molecule?

Thank you very much!

Michael

Confidentiality Notice: This message is private and may contain confidential and pro= prietary information. If you have received this message in error, please no= tify us and remove it from your system and note that you must not copy, distribute or take any action in reliance on it. A= ny unauthorized use or disclosure of the contents of this message is not pe= rmitted and may be unlawful.

--_000_6DCAB3E586E6A34FB17223DF8D8F0D3D028C7D5E93MAILBOX03unam_--