Manually creating a Z-matrix is both an useful exercise in instruction, as well as sometimes the preferred way of inputting a specific structure (especially in inorganic chemistry which is less supported by graphical tools).
The "original" babel was/is able to read Gaussian input files, although the implementation was buggy (accepts erroneous inputs). Mopac is another widely used program, using a sligthly different Z-matrix format for input.
Documentation:
Gaussian (includes sample inputs):
http://www.gaussian.com/g_ur/m_molspec.htm
http://www.gaussian.com/g_ur/g03mantop.htm
Mopac 7 is public domain, so in my understanding the code can be incorporated into anything, including GPL'ed software. Mopac 7 contains a Z-matrix to cartesian coordinate converter.
Project homepage:
http://sourceforge.net/projects/mopac7/
Z-matrix to xyz converter (in Fortran):
http://mopac7.cvs.sourceforge.net/mopac7/mopac7/fortran/gmetry.f?revision=1.1.1.1&view=markup
However, please consider this:
http://mopac7.cvs.sourceforge.net/mopac7/mopac7/COPYING?revision=1.1&view=markup
I am not sure how this text would match the notion
on "public domain".
Logged In: YES
user_id=21420
Originator: NO
MOPAC internal coordinate format is supported in version 2.1 for both reading and writing.
I don't think attempting Gaussian is such a great idea -- I've seen too many people attempting to do "clever" things with Gaussian z-matrix, such as variable substitution, etc. If you like, I'll set this feature request for Gaussian z-matrix input reading, but it would be a complicated parser.
That said, if MOPAC is sufficient for your needs, you should try the 2.1 release and the "mopin" format. Please let me know if I can close this request.
Logged In: YES
user_id=21420
Originator: NO
I've just added Gaussian z-matrix reading/writing in the Open Babel 2.2 SVN (revision 2220 or later). I'd be happy to send you the format file if you like.
I'm marking this "Pending" further comment. If not, it will close in 2 weeks as being fixed.
Logged In: YES
user_id=1312539
Originator: NO
This Tracker item was closed automatically by the system. It was
previously set to a Pending status, and the original submitter
did not respond within 14 days (the time period specified by
the administrator of this Tracker).