The follow information is reproduced from
  "Keith, J. A.;  Fantauzzi, D.; Jacob, T.; 
  van Duin, A. C. T. Phys Rev B 2010, 81, 235404"

- The force field optimization involved parameterization 
of the fcc, bcc, ideal-hcp, sc, diamond, and a15 bulk phases of Au.  
For these phases the ReaxFF force field gives good 
agreement for the binding energy, volume of minimum 
energy, and curvature of the binding well around the 
minimum compared to the QM calculations used 
for parameterization.