[molpro-user] CASPT2 without semi-internal excitations

Alexander Sokolov asokolov at uga.edu
Sat Sep 13 13:29:48 BST 2014

Thank you, Sham. I should have been more specific. I actually meant the
latter (two-electron excitations with one external label). However, it may
be enough to remove singles for my purposes.

Best wishes,

Alexander Sokolov
Postdoctoral Research Associate
Princeton University
Princeton, NJ

On Sat, Sep 13, 2014 at 6:45 AM, Sham K <shaawm at gmail.com> wrote:

>   Dear Dr.Sokolov,
>  Not sure what exactly you mean by semi-internals, different researchers
> understand it differently. In loose terms, semi-internal is just an alias
> for singles. If this is the case, then this is easy to get. After CASPT2
> calculation, the energy contributions from different spaces are printed at
> the end of iterations. If you want to eliminate singles during calculation,
> then use {rs2;nosing;}
>  By semi-internals, if you specifically mean only the two-electron
> contracted excitations with one-external label, it is then not possible to
> separate it out because molpro's CASPT2 uses uncontracted singles, unlike
> molcas CASPT2 which uses fully contracted singles.
>  Hope this helps.
>  Best wishes,
> Sham
> On Sat, Sep 13, 2014 at 6:34 AM, Alexander Sokolov <asokolov at uga.edu>
> wrote:
>>  Dear Molpro Users/Developers,
>>  I would like to compute CASPT2 energy without the contribution from
>> semi-internal excitations. As far as I understand, these excitations are
>> included in Molpro by default. Is there a way to remove their contribution
>> from CASPT2?
>>  Thank you,
>>  Alexander Sokolov
>>  Postdoctoral Research Associate
>> Princeton University
>> Princeton, NJ
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>> Molpro-user at molpro.net
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