Re: [cclib-devel] etsecs conversions

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

On Tuesday 27 of March 2007 14:38, Noel O'Boyle wrote:
> On 27/03/07, Karol Langner <kar...@kn...> wrote:
> > On Tuesday 27 of March 2007 14:21, Noel O'Boyle wrote:
> > > This code may be old and creaky, but the general idea was as follows:
> > >
> > > (1) You multiply by two because for an excitation from a
> > > doubly-occupied orbital there are two excitations in fact...one
> > > involving the alpha electron and one involving the beta electron. For
> > > an unrestricted calculation, you shouldnt multiple by two.
> >
> > GAMESS, for example, prints the excitations of both alpha nad beta
> > electrons, even for restricted calculations (see test file
> > "water_cis.out"). The coefficients alpha and beta electrons are always
> > the same.
> >
> > > (2) You square because that is the definition of etsecs. It is a
> > > somewhat arbitary definition so I am happy to change it. The idea is
> > > that these sqr values somehow represent the fractional contribution of
> > > a particular SEC to the whole transition. Unfortunately, at least in
> > > TD-DFT, this is almost but not exactly true (i.e. these fractional
> > > contributions dont add to 1). In fact, this is probably a good unit
> > > test to have to make sure that all parsers are doing the same thing.
> >
> > So we can't really test if they sum up to 1, since they don't :)
>
> Sorry - I should have been more clear. They almost sum to 1, and so an
> assertInside would still be a useful test since if the values sum to
> something quite different than 1, there is some problem. However, may
> I suggest redefining etsecs to use the original positive or negative
> coefficients. The test should use the squared values though. I know we
> shouldn't redefine the API in a point release, but I feel no
> responsibility towards API attributes that we didn't test rigourously.

OK, I understand.

> > Another point: as far as I can see, there's no way to force Jaguar to
> > print out triplet excited states.
>
> You're saying that it is possible to do the calculation, but just not
> print out the results?

No, that is a logical mistake on my part.

-- 
written by Karol Langner
Tue Mar 27 17:12:37 CEST 2007