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[Nguyen Kiet A Contr AFRL/MLPJ]

>  This is a common problem with large molecules or even not so large molecules.  A fix for this is to drop functions (or symmetry-adapted linear combination of basis functions) from the variational space. Here an example :stilbene with 6-31G(d) basis set.
> > 
> > **,stilbene
> !6-31G*memory,19.0,m;
> file,2,stbm.wfu;
> int,,cart;xy,z;
> a1,C,4.71686500,2.10056588,0.00000000
> a1,C,3.66978494,0.35056413,0.0000000
> a1,C,7.32403483,2.45884919,0.00000000
> a1,C,5.35145616,2.41458172,0.00000000
> a1,C,8.96582004,0.38358916,0.00000000
> a1,C,7.96397471,-2.05799134,0.00000000
> a1,C,0.94345995,0.85838373,0.00000000
> a2,H,8.08382633,4.36617729,0.00000000
> a2,H,4.58818346,4.32223858,0.00000000
> a2,H,10.99769087,0.67186112,0.00000000
> a2,H,9.21425535,3.68618149,0.00000000
> a2,H,3.48658504,3.74183427,0.00000000
> a2,H,0.46126873,2.85831258,0.00000000;
> S,1,3047.52488,457.369518,103.948685,29.2101553,9.28666296,3.16392696,7.86827235,1.88128854,.544249258,.168714;C,1.6,.001834737,.014037323,.068842622,.232184443,.467941348,.362311985;C,7.9,-.11933242,-.160854,1.14346;P,1,7.86827235,1.88128854,.544249258,0.168714;C,1.3,0.06899907,0.31642396,0.74430829;D,1,0.8;S,2,18.731137,2.82539,0.640122,0.161278;C,1.3,0.0334946,0.234727,0.813757;-
> ;hf;wf,96,1,0;
> > 
> > 
> > 
> > >The error message that you see is certainly driven by the lowest>eigenvalue of the basis overlap being less than 1.0d-8, and you will>find the print of the eigenvalues so tested immediately above the>error message. If this isn't the case, I guess further progress can>come only if you give your input file so that somebody can try to>reproduce it. In principle the 10^{-8} threshold could be made>adjustable, but I wonder if there is any case with a more singular>metric than this for which one could really solve the SCF equations in>64-bit arithmetic.
> > 
> > 
> > 
> > Kiet A. Nguyen, Research Scientist                  
> > AFRL/MLPJ                                            
> > Laser Hardened Materials Branch          
> > Wright-Patterson AFB, OH  45433  
> > Phone (937) 255-6671, Ext 3178
> > FAX   (937) 255-1128
> > 
> >               
> >  
> > 
>