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Re: ROUNDOFF ERROR IN BEND message when reading a Z matrix

Alex Granovsky
gran@classic.chem.msu.su


Hi Reinaldo,

On Mon Jul 26 '10 0:24am, Reinaldo Pis Diez wrote
-------------------------------------------------
>Dear folks,

>I'm using Firefly 7.1.G, build number 5618, to study a system containing about a hundred atoms. I'm using cartesian coordinates due to construction issues. Scf is ok, slow but convergent. Now, I have to optimize the neighborhood of a given atom, so I decide to use nzvar=3M-6 in $contrl, and "build" the z matrix in $zmat using zmat(1)=1,1,2, etc, etc. I've checked the z matrix and is ok with respect to connectivity issues.
>Despite the ifreez option I'm using to freeze almost all the internal coordinates, Firefly returns an error message during the reading of the z matrix in check mode:

>   --- ENCODED Z MATRIX ---
> COORD    TYPE     I    J    K    L    M    N
>     1       1     2    1
>     2       1     3    1
>...
>   309       3   105   69   33   21
> ROUNDOFF ERROR IN BEND - STOP

>where the 309th coord is the last one. What is the source of that error? (Almost) linear bond or torsion angles perhaps?

Indeed, the (quasi) linear angle is the most likely source
of this error. Try to alter your internals to avoid degenerate
angles and torsions, alternatively, you can try to use
DLCs/ifrzat array.

regards,
Alex Granovsky





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