[molpro-user] Davidson and Pople correction in MRCI

[Lorenzo Lodi]

Peter Reinhardt wrote:
> Lorenzo,
> there are several modified Davidson formulae, for instance :
> 
>   CORRECTION c_0^2/(2c_0^2 - 1)
>   E.R.Davidson, D.W.Silver, Chem.Phys.Lett 52 (1977) 403
> 

Yes, I am aware of that (I have recently read a review on the topic, 
Duch Diercksen, J.Chem.Phys. 101(4),3018 (1994) ). Anyway, looking at 
Molpro's code I'm quite sure (1-C(0)^2)/C(0)^2 is used.


> And running Gaussian with CISD in the first line, you get the same Pople
> correction
> 
> Molpro:
> 
>  Cluster corrected energies
>     -76.22423966 (Davidson)           -76.22423966 (externals)
>     -76.22181399 (Pople)              -76.22181399 (externals)
> 
[...]

I'm sorry, how did you obtain these numbers? Anyway, I must stress that 
in the case of single-reference CISD I *do* understand the values given 
by Molpro, my question regards only MRCI calculations...

Regards,

Lorenzo