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Alex Granovsky
gran@classic.chem.msu.su

indeed Hessian calculations uses symmetry and thus
are faster for symmetric structures provided you
specify the symmetry group explicitly in the input
file. Otherwise, there will not be any speedup!

Regards,
Alex


On Tue Dec 22 '09 12:07pm, Valentin Monev wrote
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>Dear all,

>I have a (planar) molecule optimized at a high (mp2/ccpvtz+) level of theory, using C1 and Cs symmetry, i.e. two optimized geometries of the molecule, in the second of which the z coordinates are not 0.00xxx but pure 0.00000.

>I know that using Cs symmetry the geometry optimizes in 7 points, while using C1 (no symmetry) takes 22 points! Delocalized coordinateds (dlc) are used in the optimizations, and "any DLCs will not be symmetry-preserving" http://classic.chem.msu.su/cgi-bin/ceilidh.exe/gran/gamess/forum/?C34df668afbHW-7293-92+00.htm
>
>If I do a hessian calculation of these two optimized molecules, at C1(no symmetry) and Cs symmetry, will it take the same time, or will the Cs calculation be faster?

>What do you think?

>Valentin