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1:05:06 PM PST  Wed, Dec 5th 2018 

Dear all,
I am trying to calculate the absorption spectrum of excited CHBr3 with an extended CBr bond. CHBr3 is in excited T2, where one HOMO1 electron is excited to LUMO. I can use the following tag to do it, however, it doesn't necessarily converge to T2 state. Sometimes, it only converges to T1 state.
vectors swap beta 55 56
MAX_OVL
Is it possible to run a first LRTDDFT calculation with tag CIVECS to export the T2 state and perform the second LRTDDFT based on the CI vectors from the first step?
If we have to revise the code, what subroutines I should revise?
Thanks a lot!




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5:50:32 AM PST  Fri, Dec 7th 2018 

No, you cannot perform a second LRTDDFT calculation with a reference built from the CI vectors of an excited state. LRTDDFT is formulated for a single determinant reference state and your T2 solution from the first LRTDDFT would be a linear combination of determinants.
Quadratic response TDDFT could give you the absorption spectrum for an excited state; however, it is not implemented in NWChem (the only implementation I am aware of is in the code Dalton).
Within NWChem, you could attempt our RTTDDFT based approach to excited state absorption ("Excited state absorption from realtime timedependent density functional theory" JCTC vol. 11 42944303 [2015] https://pubs.acs.org/doi/abs/10.1021/acs.jctc.5b00473). While not documented, the functionality for this approach is in version 6.8 of the code. You would need to first run a LRTDDFT gradient calculation on the excited state of interest in order to generate the excited state density matrix (or matrices in the case of an open shell calculation). You can then use the excited state density as your starting point by adding the appropriate load command to your RTTDDFT input block:
load density <file name>.dmat
for closed shell or
load density <file name>.dmatA <file name>.dmatB
for open shell, where you would obviously insert the file name for the density matrix (matrices) generated from the LRTDDFT gradient calculation. From there you should be able to follow the method outlined in the above cited paper to generate the absorption spectrum.

Edited On 5:52:34 AM PST  Fri, Dec 7th 2018 by Sean




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9:36:21 AM PST  Thu, Jan 31st 2019 

Hi..in my case i was trying to do excited state geometry optimization using the analytical gradient of LRTDDFT. I did not find the relevant part of the manual that describes the gradient calculation of LRTDDFT. so, I am wondering if this function available in dalton? if yes, how to use it? Thank you for your help!
https://www.7pcb.com/

Edited On 4:09:18 PM PST  Thu, Feb 28th 2019 by AvritSase




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9:29:02 AM PST  Tue, Feb 5th 2019 

Sorry I misunderstood you. Geometry optimization on the excited state is straightforward within NWChem. See the third example input in the documentation https://github.com/nwchemgit/nwchem/wiki/ExcitedStateCalculations#sampleinput



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