TDDFT error

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Hi,
I'm running a singlet TDDFT calculation with LCwPBE functional
I found a message error

' tddft_diagon: negative excitation energy 0
------------------------------------------------------------------------
------------------------------------------------------------------------
current input line :
0:
------------------------------------------------------------------------
------------------------------------------------------------------------
This type of error is most commonly associated with calculations not reaching convergence criteria'

I'm using this setting in my input

cosmo
solvent methanol
end
driver
maxiter 600
end
dft
xc xwpbe 1.00 cpbe96 1.0 hfexch 1.00
cam 0.3 cam_alpha 0.00 cam_beta 1.00
iterations 100
direct
convergence energy 1d-8
grid fine
maxiter 600
convergence damp 20 lshift .6
end
tddft
rpa
nroots 3
singlet
maxiter 600
print high
end
task tddft energy

How can I fix it?

regards

Marcel

  • Niri Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Hi Marcel,

This means that the (A-B) is not positive definite and that suggests that the singlet ground state
in your calculation is unstable to a triplet. The consequence of this is there are -ve excitations.
A workaround is via the Tamm-Dancoff approximation (keyword tda). This may solve the problem.
But I think the issue in your case is the singlet-triplet instabiity as I suggested earlier.

Feel free to send me a direct email if you want to discuss more.

Best,
-Niri

niri.govind@pnnl.gov

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Hi Niri,
Thank you for the reply.
If the problem continues, I will contact you.

regards

M.


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