[molpro-user] Counterpoise correction for Na+He

[Grant Hill]

Dear Shengfu,

I think you may have misunderstood the previous suggestions. The frozen core approximation (the default in almost all single-reference post-SCF methods) is that only valence electrons will be correlated. Na+ has zero valence electrons so in this case the CCSD program has no electrons to do anything with.

One way to remedy this is with "all-electron" calculations, where the core electrons are correlated. This can be performed in Molpro by using the core directive in your CCSD block, the wf directive will not help in this case. Of course, most basis sets (such as aug-cc-pVDZ) also assume the frozen core approximation and do not contain the tight functions necessary for a balanced description of the correlation of the core electrons. This means you should also use an appropriate basis set, such as aug-cc-pwCVDZ.

I recommend that you read the following papers on core-valence basis sets as they illustrate the problem better than I can:

J. Chem. Phys. 103 (1995), 4572
J. Chem. Phys. 117 (2002), 10548

Correlation consistent basis set for Na that contain core-valence correlating functions have not yet been published, but I believe a paper on this is forthcoming.

HTH,

Grant


On 8 Feb 2010, at 02:20, Yang, Shengfu F. (Dr.) wrote:

> Dear All,
> 
> I still have problem with the counterpoise correction for the HeNa+ complex. From the previous emails, I was suggested problem with valence and core correlations of electrons, and such basis set should be used. In addition, OCC card should be used to define the orbitals. 
> 
> The ground state of HeNa+ is WF,12,1,0; and the grant state of Na+ should be WF,10,1,0; OCC,3,1,1,0 should be the ground state occupation. Otherwise it will end up with an excited state of Na+ which is unreasonable. 
> 
> The output file is attached in this email. Can anyone take a look at it and give me some suggestion on this?
> 
> Thank you very much!
> 
> Sincerely Yours,
> 
> 
> Dr. Shengfu YANG
> -------------------------
> Department of Chemistry
> University of Leicester
> Leicester LE1 7RH
> UK
> Tel: +44-116 252 2127
> Fax: +44-116 252 3789
> -------------------------
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