[Molpro-user] how to avoid SCF restart in a CCSD(T) scan and why does the SCF converge to a wrong state?

[Kirk Peterson]

Dear Fedor,

which version of Molpro are you using?

In any event the following suggestions may help:

1) not sure what the "restart,0" line is supposed to do. Restart cards  
must always come directly after any memory cards. You don't need it  
anyway
2) your "wf" command should come in as part of the "rhf" command:
      rhf;wf,24,1,2    (all enclosed by braces if this is 2006.1 and  
above)
3) to make the rhf use the bare hamiltonian guess every time, change  
this to   rhf;wf,24,1,2;start,h0

-Kirk

PS - BTW, 450 mwords of memory (about 4GB) for this job is probably at  
least 350 mwords more than you need.

On Sep 12, 2008, at 5:32 AM, Fedor Goumans wrote:

> Dear all,
> Just getting started with molpro I wanted to use to scan PESs.
> It turns out that for this particular coordinate (see input below),
> CCSD(T) always crashes in the 2nd step, with this message:
> UNREASONABLE NORM. CALCULATION STOPPED
> In the CCSD bit of the programme.
>
> It looks like in the second step the RHF reference wavefunction
> converges to a wrong state (e.g. for the input below -187.2009 H vs.
> -187.5115 H for a 'fresh start' on the same geometry) giving rise to
> this problem, because when I scan the coordinate by hand, the RHF is
> not restarted and the CCSD converges just fine (also the RHF energy is
> lower). I am surprised that this happens even at these small step
> sizes of 0.05A. I've tried to turn off restart as in the example
> below, but the rhf is restarted every time in the second step even
> though restart,0 is in the do-loop.
>
> Any ideas about why the SCF converges to a wrong state?
> Any ideas how to switch of RHF SCF restart in a PES scan?
>
> Thanks in advance for your help.
>
> Fedor Goumans
>
> Example input for scan:
>
> ***,O+CO long range complex
> memory,450,m
> DR=0.05
> do i=1,40
> restart,0
> r2=2.0+i*dr
> r1=1.13599229
> a1=120.0
> geometry={Y
> angstrom;
> O1;
> C,O1,r1;
> O2,C,r2,O1,a1;
> }
> basis=cc-pVDZ
> wf,22,1,2 ! A' surface
> rhf
> rhf-uccsd(t)
> enddo
> ---
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