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

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

On Tuesday 27 of March 2007 19:55, Karol Langner wrote:
> But, there seems to be a problem related to the excitation coefficients
> (which need a tolerance above 0.0005, by the way). Namely, some of the
> coefficients printed by Gaussian have different signs than the ones printed
> by GAMESS (observe also that the ones given by Jaguar are consistently with
> an extra minus compared to GAMESS). This is probably due to the symmetry
> type (A1, B1, A2, ...). I don't know what the relation is, however, and we
> should standardize this. Any ideas? Notice that the appropriate new test in
> testCI.py fails.

After some thought and conversations with colleagues, I can't think of any 
physical/chemical reason that the coefficients would have different signs. 
After all, only their squares have meaning in terms of the Hamiltonian - so 
their sign could be the byproduct of numerical assumptions in the code.

The sign, however, should influence the transition moments and so also the 
oscillator strengths. 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.

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?

Karol

-- 
written by Karol Langner
Wed Mar 28 01:06:11 CEST 2007