View source for 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<ref>[https://pubs.acs.org/doi/abs/10.1021/jp012125b H. P. Hratchian and H. B. Schlegel, J. Phys. Chem. A 106, 165 (2002).] </ref>. 
*{{TAG|IRC_DIRECTION }} direction of the initial displacement (-1|1 – negative|positive)
*{{TAG|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,  {{TAG|IRC_STOP}} should always be greater than 1. 
*{{TAG|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)
*{{TAG|IRC_MINSTEP}} =    0.0250
*{{TAG|IRC_MAXSTEP}} =    3.0000
*{{TAG|IRC_VNORM0}} =    0.0020

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



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