Subject: Re: CCL:Slater Basis Set

From: Stan van Gisbergen <vgisberg.-at-.few.vu.nl>
Date: Thu, 21 Oct 2004 08:41:15 +0200

Dear Dr. Boufarik,

The Amsterdam Density Functional program (ADF, www.scm.com) uses Slater 
orbitals.
Over the years, we have received several comments from ADF users around 
the world claiming
that Slaters indeed have important practical advantages over Gaussians 
in several situations,
including:

- smaller Basis Set Superposition Errors (BSSEs), perhaps due to the 
correct cusp behavior.

- better description of weak interactions, due to the better 
description of the tails in the outer region.

- there are fewer Atomic Orbitals that give a sizable contribution to a 
particular Molecular Orbital.
   This makes it much easier to qualitatively understand the nature of 
the MO.

These are some of the reasons why the difference between Slaters and 
Gaussians can indeed be
of chemical relevance. Of course, some of the problems with Gaussian 
basis sets can either be
corrected for or be circumvented by choosing a (much) larger basis set, 
which obviously has other
drawbacks.

Best regards,
Stan van Gisbergen

PS. A side remark:
If one constructs an xc potential that exactly reproduces a Gaussian CI 
density, this xc potential will
contain spurious oscillations and incorrect asymptotic behavior, unless 
additional constraints are
imposed. This is a direct negative effect of the shape of the Gaussian 
orbitals.

P.R.T. Schipper, O.V. Gritsenko & E.J. Baerends
Kohn-Sham potentials corresponding to Slater and Gaussian basis set 
densities
Theor. Chem. Acc. 98 (1997) 16-24

On Oct 19, 2004, at 9:34 PM, A. Boufarik wrote:

> Greetings all,
>  
> In the past years, I have seen many people trying to use Slater 
> orbitals as a basis set in the molecular calculations. Two main 
> arguments have been put forward:
> [1] Theoretical: Shrodinger equation has solutions that are closer to 
> Slater orbitals that Gaussians. As an example, hydrogen functions all 
> have an exponential terms exp(-x) rather than exp(-x*x)
>  
> [2] Practical : It has been argued that for CI calculations, we better 
> have a small basis set so to allow scan larger configurations spaces.
>   
> Two questions are in my mind : 
>   
> [1] Have any of the Gaussian experts met a problem for which the basis 
> was too large to be handled during CI. Something that may support 
> statement (2)
>  
> [2] From a chemistry point of view, is there any benefit for using 
> Slater orbitals. I mean by this, will there be any new 
> physics/chemistry that can only be detected by a Slater basis. Or, is 
> this just another way to do the same old chemistry with an extra 
> 10^(-15) accuracy instead of 10^(-13) with gaussians.
>  
> Thanks for your comments and ideas,
>  
> Boufarik 

Dr. S.J.A. van Gisbergen  
Chief Executive Officer     
Scientific Computing & Modelling NV
Theoretical Chemistry, Vrije Universiteit
De Boelelaan 1083
1081 HV Amsterdam
The Netherlands                              
T: +31-20-4447626    
F: +31-20-4447629        
vangisbergen.-at-.scm.com  
http://www.scm.com