[molpro-user] Basis Set Confusion

[Kirk Peterson]

Dear Frank,

no worries, these two "versions" of aug-cc-pV5Z are exactly equivalent  
to each other. On the EMSL
website there is a radiobox that by default is checked called  
"optimize general contractions". This exists
for programs like Gaussian that can not exploit generally contracted  
basis sets. This option essentially
just deletes from contractions primitives that are also uncontracted  
in the basis. Davidson discusses
this strategy in  Chem. Phys. Lett. 260, 514 (1996). If desired, you  
can obtain the exact same basis set as Molpro
by unchecking this box.

On a related note, for second row atoms it is highly recommended to  
use the so-called +d basis sets,
aug-cc-pV(n+d)Z.  I would guess for your AlCl3 case they will give  
much improved convergence at least
for your structural parameters and probably your energetics as well.   
These of course are available
within Molpro or from EMSL.

best regards,

Kirk

On Oct 23, 2009, at 11:46 AM, Frank Uhlig wrote:

> Dear Molpro-Users,
>
> I have a question concerning the by Molpro provided Dunning aug-cc- 
> pV5Z
> basis sets for aluminum and chlorine (Molpro Version 2008). While  
> trying
> to perform CBS evaluations for AlCl3 I found that there is a  
> difference
> concerning the contraction of the first three s functions. While in  
> the
> Molpro basis set library 20 of 21 primitives get contracted to
> respectively one s-function the by the EMSL provided basis sets show  
> for
> the same functions only 16/21 contracted primitives. The contraction
> coefficients of each primitive contracted in both cases are the same.
> Thus I am wondering what lead to this difference and would appreciate
> any further information.
>
> Best regards,
>
> Frank Uhlig
>
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