Intrinsic-reaction-coordinate calculations

The potential energy profiles along intrinsic reaction coordinate (IRC) can be computed via damped velocity Verlet algorithm of Hratchian and Schlegel.

Experienced users can affect the performance of the dimer method by modifying the numerical values of the following parameters (the given example values are the default values):

• IRC_DIRECTION direction of the initial displacement (-1|1 – negative|positive)
• IRC_STOP = 20 the number of steps the energy must monotonously increase, used as a termination criterion for the DVV procedure (going from TS you expect to decrease energy till you reach a minimum (that’s the time to stop) and then energy increases again). In order to avoid a premature simulation termination (especially close to TS, i.e. at the very beginning of simulation), e.g., due to a numerical noise, DVVEHISTORY should always be greater than 1 (10-50 usually does the job)
• IRC_MINSTEP = 0.0250
• IRC_MAXSTEP = 3.0000
• IRC_VNORM0 = 0.0020
• IRC_DELTA0 = 0.0015