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Article ID: 826 - Last Modified:

I am running an IRC calculation with Jaguar, but it is failing. What could be causing this?

IRC calculations can fail when the gradient is too small to locate the next IRC point. If the potential energy surface is flat, you can use the gen section keyword, ircgcut, to set a factor for the gradient threshold. A reasonable range is 0.1 - 0.5. However, if the threshold is below the noise level in the gradient, the results will be unpredictable. If you use this keyword, you should ensure that you have accurate gradients, by setting iacc=1 and using the fine DFT grids in DFT calculations. If the surface is very flat, a value below 0.1 can be used with accurate grids (gdftmed, gdftfine, gdftgrad set to 13).

Keywords: Jaguar, gradients, intrinsic reaction coordinate

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