| 10:08:22 PM PDT - Thu, May 21st 2015 |
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If you enumerate and locate all the atoms in a compound, then you can't use symmetry point groups, only C1 symmetry.
In Principle, you may specify methane using Td symmetry and need only state the coordinates of
Carbon at (0,0,0) and
Hydrogen at (0.6276,0.6276,0.6276)
The justification is that an optimization using symmetry converges faster. You can describe benzene as 12 atoms in a C1 group or two atoms in a D6h group. The latter is significantly quicker to converge ... if you can describe it correctly.
In Practice, I use C1 symmetry by default according to the Principle of Maximum Laziness, a 1st Law corollary, and try to use Z-matrix form for molecules having more than 3 atoms.
Kill Specify them all and let God NWChem sort it out.
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