The Intrinsic Reaction Coordinate method pioneered and developed by Mark Gordon, North Dakota State University, has been incorporated into MOPAC in a modified form.
The Dynamic Reaction Coordinate is the path followed by all the atoms in a system assuming conservation of energy; i.e., as the potential energy changes the kinetic energy of the system changes in exactly the opposite way so that the total energy (kinetic plus potential) is a constant. It is equivalent to the molecular mechanics molecular dynamics calculation, except that bond-breaking and bond-making are supported, as are all the electronic phenomena of the semiempirical methods.
If started at a ground state geometry, no significant motion should be seen. Similarly, starting at a transition state geometry should not produce any motion--after all it is a stationary point and during the lifetime of a calculation it is unlikely to accumulate enough momentum to travel far from the starting position.
In order to calculate the DRC path from a transition state, either an initial deflection is necessary or some initial momentum must be supplied.
Because of the time-dependent nature of the DRC the time elapsed since the start of the reaction is meaningful, and is printed.