Subject: G03: LANL2DZ basis set for Se Te...

From: Wai-To Chan <chan/at/curl.gkcl.yorku.ca>
Date: Thu, 5 Aug 2004 03:53:14 -0400 (EDT)

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Hello CCLers

I get the following warning while using LANL2DZ basis set for Se or
(Te) atom  in Gaussian 03.

" Warning!  Se atom    1 may be hypervalent but has no d functions."

In the Gaussian book (Exploring Chemistry.. Foresman and Frisch) I saw
something about  adding diffuse functions manually with a file called
"plus.gbn"

do I have to add  d functions manually?  or is the LANL2DZ basis set
good enough. I am mainly interested in the structure of molecules like
(H2SeO4)

I saw a thread titled "generating or augmenting basis sets" from last
year on ccl.net but could not find the answer. Thanks a lot for your
help

  I've used ECP basis sets like lanl2dz and SDD for transition metal
and main group elements. I don't recall ever seeing messages
like this. I guess the warning is caused by the unsually large number
atoms linked to the Se atom.  

  I've read reports of lanl2dz calculations involving augmentation
of the ECP basis with polararization and diffuse function. But 
I can't think of a source of the additional basis functions to
use. Gaussian has full-electron basis set like 6-31+G(d,p) 
for Se but I don't know if transferring the d function to 
lanl2dz is a good idea.

In case that is what you want the way 
to do this is simply using the option "extrabasis" to 
add the extra basis functions to the specified 
atom. The older versions of gaussian come in with 
a basis set library which you can easily look up for the 
exponents of the polarization and diffuse functions.
With the recent versions you have to extract the basis
set information manually. 

  As an illustraction if I want to augment Se with 
the d function from 6-311G** I will first run a job like 

rhf/6-311G(d,p) gfinput (or gfprint) 

on the above molecule. The gfinput option will
print out the basis set details in a convenient 
format.  I will then run a job like 

rhf/lanl2dz extrabasis 

  This extrabasis option requires you to append the
basis function details to the end of your input file. 

  Without any augmentation lanl2dz and SDD will use the 
D95 basis set for the light atoms. So you may consider 
the use of polarization functions
> from D95** instead of 6-31+G* or 6-311+G*. My experience
is that augmentation of the light atoms alone with polarization 
functions from D95** generally results in significant improvement
of the performance of the ECP basis for geometry optimization 
particularly on the bond distance between the heavy
atom and the ligand. But I don't know what the appropriate approach
is for the augmentation of the heavy atom. 

Wai-To Chan