When BIGCYCLES=n is specified, a maximum of n complete geometry optimizations are allowed. After n optimizations, the calculation is stopped in the same manner as when the allowed time is exceeded.

In a DRC, BIGCYCLES=n will run until n complete oscillations have occurred.   BIGCYCLES=1 would allow a single complete vibration to be generated. In simulated annealing or heating, see DRC=n.nn, use BIGCYCLES=nnn as a guide, in arbitrary units, of how long the run should last.

BIGCYCLES is useful in comparing calculations using different computers. Different machines run at different speeds, so calculations based on time should not be used. Instead, by using BIGCYCLES, a specific number of cycles can be run, regardless of the machine speeds.

See also CYCLES and T=n.nn