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

[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}