Subject: ADF: AE-Fit-functions (answer)

From: [email-masked] (Christoph Schwittek)
Date: Wed, 13 Aug 1997 15:02:17 +0100 (NFT)

original question:

>Has anybody developed fit-functions for the all-electron-basis
>to be used in ADF? I ask this question because we would like to
>do a geometry-optimization in an electric field by hand (coordinate 
>driving) In our opinion it is important to take into account the
>inner shells too to explain a molecular electrostriction.
>Are there other opinions? 

answer:

>   Two comments on your question. First,  you can make the fit basis
>yourself. Any combination of two basis functions contributes to the
>density, and hence must be represented by the fit basis. For instance,
>if your basis has two p-sets with coefficients alpha1 and alpha2,
>then there is a d-type contribution in the density with coefficient
>alpha1 + alpha2 that must be represented by the fit basis (in fact,
>there are two more d-type contributions, with coefficients 2*alpha1
>and 2*alpha2). We had in Calgary an old utility program with ADF
>that would calculate from a given basis set all the possible combinations
>for the fit and their respective overlap, so that one can choose a reasonabl=
e
>fit basis from that. The program is called "alphas" -- maybe you can
>obtain it or its successor from Amsterdam. I have occasionally
>created basis sets with smaller cores, and consequently had to
>make a new fit basis each time.
>   Second, as you know, ADF uses numerical integration throughout.
>While this works well normally, I would be careful with all-electron
>calculations of heavy atoms because the very steep density near
>the nucleus might well strain the integration scheme over the limit,
>at least this was my experience sometimes. Admittedly, I haven't
>played with the detailed integration parameters here, and one can
>probably do a lot by just increasing the integration accuracy around
>the nuclei only.
>
>Hope this helps a little...
>
>Viele Gr=FC=DFe von Georg
>
>--
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>Dr. Georg Schreckenbach           Tel:     (USA)-505-667 7605
>Theoretical Chemistry T-12        FAX:     (USA)-505-665 3909
>M.S. B268, Los Alamos National      E-mail:  [email-masked]
>Laboratory, Los Alamos, New Mexico, 87545, USA
>Internet:    http://www.t12.lanl.gov/~schrecke/
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
Thank you for your hints, Georg!
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 -                 Dipl.-Phys.  Christoph Schwittek                    -
 -                                                                     -
 -             email: [email-masked]              -
 -              Organische Strukturchemie,  Ak Bleckmann               -
 -                       Universitaet Dortmund                         -
 -                        Otto-Hahn-Strasse 6,                         -
 -                          D-44227 Dortmund                           -
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