Subject: Question about TDDFT/B3LYP and conjugated polymer

From: Zhu ZX <zzxccl{at}yahoo.com>
Date: Sat, 12 Jul 2003 23:25:21 -0700 (PDT)

Hi all,
   My present problem is about the TDDFT with B3LYP functional and conjugated polymer. I did some investigate on some derivations of pyrrole and thiophene oligomers using TDDFT with B3LYP functional. The band gaps(transition energy from the ground state to the first dipole-allowed excited state) of the corresponding polymers obtained by oligomer extrapolation are in good agreement with the experimental data within 0.15ev. But the conventional functionals are local(the potential is a function of the local density or the local gradient) and are not suited to describe delocalized features. This can lead to severe errors in the simulation. (see CHEMPHYSCHEM 2003,3,292) However, some reports also considered the TDDFT with B3LYP is a relatively reliable tool for evaluating of the transition energies of low-lying excited states.(J Phys.Chem.A 2001,105,451; J Chem. Phys. 1998,108(11),4439) Now I want to know why the TDDFT/B3lyp does not suffer from the drawbacks of local approximations to
 describe the ultranonlocal features.  Thank you very much!
Sincerely yours,
Su Xing 
zzxccl{at}yahoo.com

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