Anomalous behavior of Gear's predictor-corrector algorithm in a molecular dynamics simulation of amorphous silicon

An anomalous behavior of Gear's predictor-corrector algorithm is observed during a microcanonical molecular dynamics simulation of amorphous silicon. While the amorphous silicon network generated by quenching was being annealed, an anomaly is started: both the total energy and the temperature of the system spontaneously and indefinitely increased, in violation of energy conservation. No such phenomenon was observed when the integrator was switched to the Verlet algorithm. To remove this anomaly with the Gear's algorithm, it was necessary to reduce the size of the time step to 1/32 of the 'usual value (∼ 1/100 of the fastest vibration period in the system)' at least. Our results show that Gear's algorithm may become very unstable in a realistic simulation when the time step is not small enough, that is, orders of magnitude smaller than conventional value.