Re: [cclib-devel] oscillator strengths/transition dipoles (was: etsecs conversions)

[Karol L. <kar...@kn...>]

On Wednesday 28 of March 2007 10:36, Noel O'Boyle wrote:
> > The sign, however, should influence the transition moments and so also
> > the oscillator strengths.
>
> Are you sure? In my mind, the secs are a mathematical construction
> that gives a solution to the TD-DFT or CI calculation. It is the sign
> of *this* single solution that is important. After all, there is a
> single oscillator strength associated with the solution, not several
> oscillator strengths, one for each sec. Again, I don't know much about
> this. :-)

No, I'm not sure. In any case, I guess then that it makes sense to test only 
the absolute values of the coefficients, which is what I will do.

> >I'm not too surprised that Gaussian and GAMESS give
> > entirely different trnsition dipoles and oscillator strengths (compare
> > the water_cis jobs in both programs). An I mean entirely - Gaussian often
> > gives zero (0.0000) where GAMESS gives significantly non-zero numbers. In
> > Jaguar, again different numbers - although here they qualitively agree
> > with those in GAMESS and so might result from numerical differences. I
> > don't understand this, or I'm not reading the numbers right.
>
> I think we're hitting the limit of our knowledge here. :-)

Very true :) I'd like to push my limit a little bit further in this topic, 
though.

> > These considerations may not be what cclib is about, but I guess it's
> > important for cclib to parse consistently - and probably to only parse
> > things that are consistent?
>
> The first is true, but I don't agree with the second. Different
> programs might simply be using different algorithms to calculate the
> same quantity. What we want to do is to take that information and
> present it faithfully to the user so that they can analyse it. It is a
> different question to compare and contrast the output of different
> comp chem packages...perhaps that's another paper (although I
> recommend reading the Gaussian license first of all)!

Point taken. I'm aware comparing timings of Gaussian with other programs is 
not allowed, what about calculations results themselves? I've seen a few 
articles that make such comparisons.

-- 
written by Karol Langner
Wed Mar 28 15:05:07 CEST 2007