[molpro-user] 0.1 h differences in HF energy with and without symmetry

[Hans-Joachim Werner]

Either you found a wrong state when using symmetry (wrong occupations),
or the calculation did not converge. Using Version 2009.1 (patchlevel  
21)
I found that  shift,-0.5,-0.5 helps to reach convergence, and then one  
gets the
same energy (-191.29326461) with and without symmetry. In the  
calculation with
symmetry it automatically finds the correct ground state (symmetry 2).  
In cases
where the Aufbau principle does not work correctly it may be helpful to
specify the wavefunction symmetry and the occuptions; in the present
case the input should then read

{hf;occ,13,3;closed,13,2;wf,31,2,1;shift,-0.5,-0.5}

but - as already mentioned,

{hf;shift,-0.5,-0.5}

also works in the present case. Note that the latter input would not  
work with
older Molpro versions, which always assumed wavefunction symmetry 1
if no wf card was given.

Joachim Werner


Am 26.10.2009 um 19:22 schrieb Benj FitzPatrick:

> Hello,
> I found convergence issues with the below molecule when using large  
> basis sets
> (> aug-cc-pvtz), and in trying to understand that I found that I get  
> very
> different HF energies (> 0.1 h) when symmetry is used (Cs) versus  
> when nosym is
> specified.  More specifically, nosym gives lower energies by more  
> than 0.1h.  I
> haven't noticed this problem with any of the 20 other intermediates  
> in this
> system.  I performed similar calculations using g03's ROHF and it  
> gives the same
> energy as I get without symmetry in molpro.  I also used MCSCF to  
> look for
> low-lying excited states, and there aren't any.  Is this just a  
> problem case for
> molpro's UHF/ROHF or is something more insidious going on?
> Thanks,
> Benj FitzPatrick
> University of Chicago
>
> ***,rohf sp of int7 from c3h5o-int7-cis-cis-eq_opt-ccsd-avdz-vtight- 
> a.log***
>   memory,100,M
> gthresh,oneint=1.d-12,twoint=1.d-12,zero=1.d-12
>
> hc2=1.09590208
> hc3=1.09184279
> hch3=116.45662125
> cc4=1.39830438
> cch4=122.79284718
> dih4=180.
> hc5=1.09513808
> hcc5=118.60649215
> dih5=0.
> cc6=1.39907689
> ccc6=126.2456274
> dih6=180.
> oc7=1.3692314
> occ7=125.04755482
> dih7=0.
> ho8=2.04723683
> hoc8=29.55891751
> dih8=180.
> ho9=0.9660072
> hoc9=109.16122263
> dih9=0.
>
> geometry={
>    ang;
>   nosym;
> C;
> H,1,hc2;
> H,1,hc3,2,hch3;
> C,1,cc4,2,cch4,3,dih4;
> H,4,hc5,1,hcc5,3,dih5;
> C,4,cc6,1,ccc6,3,dih6;
> O,6,oc7,4,occ7,1,dih7;
> H,7,ho8,6,hoc8,4,dih8;
> H,7,ho9,6,hoc9,4,dih9;
> }
>
>   basis=6-31G*;
> {hf;
>   wf,31,1,1}
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