Center of Mass for molecule in Gaussian09

Gaussian09 prints coordinates where the local coordinate system as center at

$C = (\Sigma n_i*X_i)/(\Sigma n_i)$

where $n_i$ is the Mass Numer of the atom. However, the Mass Number is not actually the mass of the nucleus. If we instead choose $m_i$, the true mass of each atom, as the weighting factor, we do not get the origin as the center of mass.

Is it ok to choose the origin that Gaussian09 gives us as the center of mass? Why or why not?

• Is it okay in what sense? It is certainly legal for you to do so in most countries... – Jeff Apr 8 '14 at 18:07
• When you make an optimization, you do need to be very accurate, just enough that the molecule doesn't fly away. If you do frequency calculations, later you make a couple of transformations to remove translational and rotational freedom from the Hessian, so again, it will not mater much. – Greg Jul 1 '14 at 18:18