How to Perform a UFF Calculation

You have to generate cartesian coordinates (file coord), nothing else. You can start an single-point calculation calculation by typing

uff

To start an uff geometry optimization, one has to change the number of cycles (parameter maxcycle) in the block $uff in the file control. The ouput is the optimized structure (file coord), the analytical gradient (file uffgradient) and the analytical cartesian hessian (file uffhessian0-0). Furthermore the control file will be modified:

$forceinit on
  carthess
$uffhessian file=uffhesian0-0

These commands have the effect to inititialize the force constant matric for a geometry optimization with the hessian one.

In some cases uff cannot recognize the connectivity, then one can specify the connectivity in the file ufftopology. The program will calculate the bond, angle, torsion, inverison and non-bonded terms (force field terms) based on the connectivity specified in the topology file.