Intrinsic-reaction-coordinate calculations

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Revision as of 11:15, 7 December 2022 by Tbucko (talk | contribs)

The potential energy profiles along intrinsic reaction coordinate (IRC) can be computed via d method of Hratchian and Schlegel[1]. The algorithm starts from transition state and propagates the system via damped velocity Verlet algorithm. The damping is realized via rescaling the velocity vectorto a constant value () after each propagation step.

  • IRC_DIRECTION direction of the initial displacement (-1|1 – negative|positive)
  • IRC_STOP = 20 the number of steps the energy must monotonously increase before the algorithm terminates. In order to avoid a premature terminations, especially close to transition states., e.g., due to a numerical noise, IRC_STOP should always be greater than 1.
  • IRC_DELTA0 = 0.0015 the desired error – the smaller value, the closer the computed trajectory follows the true IRC (but the more DFT steps is needed)
  • IRC_MINSTEP = 0.0250
  • IRC_MAXSTEP = 3.0000
  • IRC_VNORM0 = 0.0020 the value of in Å/fs


Mind: This method is presently available only for fixed cell shape (i.e., ISIF = 2) simulations.
Mind: The calculation must be initialized from a very well relaxed transition state (EDIFFG = -0.005 or less in absolute value).