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Re^3: Regarding using different functionals for TDDFT calculations

Alex Granovsky

Dear Siddheshwar,

in most situations, people just uses the same functional throughout.
Nonetheless, there are some known weaknesses of TDDFT in combination
with most widely used functionals e.g. as applied to charge-transfer
excited states. Here one normally uses different functionals in
optimization of ground and excited states e.g. B3LYP for ground state
and BHHLYP (or CAM-B3LYP)for charge-transfer excited states. So the
answer is: you normally need to have some specific reason when using
different functionals for different parts of computations.

Kind regards,
Alex Granovsky

On Wed Sep 17 '14 9:27am, Siddheshwar Chopra wrote
>Dear Sir,
>First of all many thanks for clearing this doubt. A little modification to this question now. DO we use the SAME FUNCTIONAL for optimization of both the GROUND AND EXCITED STATE?? What you said earlier seemed like we just need to find a better combination to get better result. The only motivation to know these things is that it is computationally very taxing to search for optimized geometry...And seems to be more taxing for optimization of excited state..
>So at times I prefer to use same functional for optimization of both S0 and S1 states, however for finding the excitation and deexcitations, I use different functionals. Is it fine Sir?
>Kind Regards,
>On Tue Jul 1 '14 3:04pm, Alex Granovsky wrote
>>Dear Siddheshwar,

>>On Tue Jul 1 '14 1:23pm, Siddheshwar Chopra wrote
>>>Dear All,
>>>I need to know: If I wish to compare TDDFT calculations from different functionals like B3LYP, PBE0 etc., then is it necessary that I MUST run the optimization/hessian with the SAME functional?

>>Strictly speaking it is not necessary to use the same functionals.
>>Assume functional A can predict equilibrium geometries
>>better than functional B while excitation energies can be better
>>with B. Then it would be logical to use A for ground state
>>geometries and B for excitation energies.

>>>Also, if I optimize with say 6-31G basis set, then can I compare the 6-31G and 6-31G (d,p) TDDFT results using the same optimized structure from 6-31G?

>>Once again, this is not absolutely necessary but most people prefer
>>to use the same basis sets.

>>Kind regards,
>>Alex Granovsky

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