Firefly and PC GAMESS-related discussion club

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Alex Granovsky
gran@classic.chem.msu.su

Linear bends in Firefly (as well as in GAMESS (US)) are strange
and odd beasts. Generally, I would not recommend to use them.

Constructing good z-matrix for such degenerate and
pathological cases as this molecule is could be a bit tricky.
Attached please find the example of good coordinates.

Regards,
Alex Granovsky



On Sun Jul 10 '11 7:54am, Alexander V. Malutin wrote
----------------------------------------------------
>Hi. I'm constantly getting bored by strange problems with $LIBE group. Every time i try to optimize molecule with linear bended region in internal coordinates, geometry search is almost constantly failing to locate stationary point then i'm using OPTTOL=1d-5 or below. Visualization of search steps shows oscillatory behavior near linear bend geometry, so i'm pretty much convinced that using linear bend $LIBE group is essential. However then i do use it, it results in error on the first step:

>          TRANSFORMING DISPLACEMENT FROM INTERNALS TO CARTESIANS
>          THE ROOT MEAN SQUARE ERROR IN ITERATION   1 IS   0.00004979
>          THE ROOT MEAN SQUARE ERROR IN ITERATION   2 IS   0.00006993
>          THE ROOT MEAN SQUARE ERROR IN ITERATION   3 IS   0.00013865
> *** ROUNDOFF ERROR IN LIBE - TEST,DOTP=   -0.2563072398E-06   -0.7003238419E-03

>How can i solve this problem? May be i am missing something and should supply input files with some special keys to avoid such errors? As far as i can see such errors have unpredictable character, sometimes $LIBE supported input works just fine, but very often run fails due this nasty roundoff problem, witch is extremely annoying. Will grateful for any help regarding this matter.

>Best regards
>Alexander

>Input file:

> $SYSTEM MEMORY=128000000 $END
> $CONTRL SCFTYP=MCSCF RUNTYP=OPTIMIZE $END
> $CONTRL UNITS=ANGS MULT=1 NZVAR=8 $END
> $BASIS GBASIS=N31 NGAUSS=6 NPFUNC=1 NFFUNC=1 $END
> $MCSCF CISTEP=GUGA FULLNR=.TRUE. FORS=.FALSE. $END
> $DRT GROUP=C1 SOCI=.TRUE. NMCC=5 NDOC=6 NVAL=3 NEXT=2 $END
> $STATPT NSTEP=100 OPTTOL=1d-6 HSSEND=.TRUE. $END
> $FORCE NVIB=2 VIBANL=.TRUE. PURIFY=.TRUE. TEMP(1)=0.001, 298.15, 398.15 $END
> $GUESS GUESS=MOREAD NORB=67 $END
> $DATA
> Cyanamide NH2-CN MCSCF.
> C1
> N           7.0   0.0000000000   0.0000000001   1.2870668159
> C           6.0   0.0000000001   0.0000000033   0.1424955716
> N           7.0   0.0000000000  -0.0000000042  -1.1681804833
> H           1.0  -0.0000000001   0.8498848363  -1.6742591359
> H           1.0  -0.0000000001  -0.8498848188  -1.6742591918
> $END
> $ZMAT IZMAT(1)=1,1,2, 1,2,3, 1,3,5, 1,3,4,
>2,2,3,5, 2,5,3,4, 3,2,3,4,5, 5,1,2,3 $END
> $LIBE APTS(1)=1.0,0.0,0.0 $END
> $VEC
> ....
> ....
> ....
> $END  

This message contains the 22 kb attachment [ patho.rar ] Sample of good Z-matrix for Cyanamide