Re: [cclib-devel] etsecs conversions

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

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 :)

Another point: as far as I can see, there's no way to force Jaguar to print 
out triplet excited states.

Karol

-- 
written by Karol Langner
Tue Mar 27 15:25:35 CEST 2007