Q: How can I carry out a geometry optimization if define fails to generate a full set of internal coordinates?
A:
Use internal redundant coordinates by using the ired command in the coordinate main menu in DEFINE.
Two other possibilites are to construct internal coordinates by hand (and check with DEFINE that they are linearly independent) or to use Cartesian coordinates (which will make the optimization considerably slower) by setting
$optimize
internal off
redundant off
cartesian on
in the control file.
