Jmol is a Graphical User Interface for Computational Chemistry

 
Jmol is free and can be downloaded.

How to use Jmol to visualize MOPAC output files:

1. Insert the keyword GRAPHF in your MOPAC2009 .mop file.
2. Run your MOPAC2009 calculation. An .mgf file will be also produced, along with the .out and .arc files.
3. Open the .mgf file in Jmol.

Warning: the bond connection algorithm of Jmol may not work efficiently with some high coordination number lanthanide complexes. Some coordinating bonds may not appear, while sometimes some other spurious bond connections may also appear. However, the positions of the atoms are always correct.