DRC=n.nnn

In a DRC calculation, the 'half-life' for loss of kinetic energy is defined as n.nnn femtoseconds. This is equivalent to the system cooling down. If the 'half-life' is negative, energy will be added to the system. This is equivalent to heating it up. If n.nnn is set to zero, infinite damping simulating a very condensed phase is obtained.

 

Here is an example of simulated annealing:

 DRC=50 bigcycles=1000 T-priority
Formaldehyde, starting with the C=O bond stretched by ~0.2 Angstroms
 
  O     0.0 +0    0.0 +0    0.0 +0                      
  C     1.4 +1    0.0 +0    0.0 +0     1     0     0      
  H     1.1 +1  121.0 +1    0.0 +0     2     1     0      
  H     1.1 +0  121.0 +0  180.0 +0     2     1     3        
As usual, the plus "+" signs are optional, the optimization flags will be ignored, and the coordinates will be converted to Cartesian at run-time.

DRC=50 - The half-life for cooling is 50 fs.

bigcycles=1000 - Restrict the run. If this keyword is not present, the job will produce a very large output.

T-priority - There are two common styles for monitoring a DRC, time and motion.  In this case time is used.