Subject: Re: CCL:TDDFT

From: elewars <[email-masked]>
Date: Sat, 05 Apr 2003 11:44:30 -0500

2003 April 5

Hello,

Re the four questions below about TDDFT:

1)  Yes, G98W does TDDFT. Try for example

--------------------------------
%Mem=100000000
%rwf=a,240mw,b,240mw,c,240mw,d,240mw,e,240mw,f,240mw,g,240mw,h,-1
#  B3P86/6-311++G**  TD=(singlets, NStates=6) Maxdisk=15360MB

 Oxiranylidene, calculating UV. Input: MP2/6-31G(df,p) geom.

 0 1
    O1        0.000000    0.778498    0.000000
    C2        0.547618   -0.593873    0.000000
etc, etc
--------------------------------------------

to calc the lowest 6 singlet states of a molecule. The rwf line probably
isn't needed here, as scratch space should not be a problem. For the
implementation of TDDFT in Gaussian see
R. E. Stratman, G. E. Scuseria, and M. J. Frisch, J Chem Phys, 1998,
109, 8218.

2) Functionals and basis sets: K. B. Wiberg, R.E. Stratman, and M. J.
Frisch, Chem Phys Lett, 1998, 297, 60. They used five functionals and
five basis sets. The results were not strongly dependent on the
functional, but B3P86 seemed best and B3LYP worst. the 6-311++G** basis
was recommended. I have found AM1 geometries to give nearly as good
results as the MP2/6-311+G** geometries used in this paper.

3) In calculations on methylenecyclopropene using
RCIS/6-31+G*//B3LYP/6-31G*, ZINDO//AM1, and TDDFT with
B3P86/6-311++G**//AM1, I found that only TDDFT matched experiment fairly
well.

4) The best caveat is perhaps to first do some calculations on molecules
related to those you're interested in and for which you know the
experimental results. This will give you a sense of how good the
calculations are. Another good idea is to read: J. Fabian et. al.,
THEOCHEM, 2002, 594, 41-53 (a critical evaluation of methods of calc
electronic spectra).

=========================
"Shobe, Dave" wrote:

>
>
> Time-dependent density functional theory (TDDFT) has become popular
> for determining electronic excitation energies (approx. = lambda max
> in UV-visible spectroscopy) and excited state properties.  I know very
> little about this other than the name, but I would like to learn.  So
> here are my questions.
>
> 1. First, can one do TDDFT calculations using G98W?  There is a TD
> command listed in the manual.  I suppose that your route card would be
> something like this:
>
> # TD B3LYP 6-31G**  (?)
>
> 2. I normally use the hybrid functional B3LYP for ground state
> calculations, as it seems to be one of the better functionals for that
> purpose.  But would a different functinoal be recommended for TDDFT
> calculations?
>
> 3. How good are the results compared to the CIS method?
>
> 4. What caveats and common beginners' mistakes are there with TDDFT?
>
> I will post a summary if there is interest.
>
> --David Shobe
> Süd-Chemie Inc.
> phone (502) 634-7409
> fax   (502) 634-7724
> email  [email-masked]
>
> Don't bother flaming me: I'm behind a firewall.
>