What do I do if my Jaguar optimization stops with the message: "stopping now - optimization seems to be stuck"?

When the potential energy surface for a molecule is nearly flat, as happens with intermolecular complexes and molecules with easily rotatable groups like methyl and cyclopentadienyl rings, noise in the gradient calculation causes the optimizer to have difficulty locating the minimum. To solve this problem, increase the accuracy in the calculation. You can do this by using the restart file to restart the job, and increase the accuracy by including the iacc=1 keyword. If you are using DFT, increase the grid density by using the following set of keywords:

gdftmed=-13 gdftfine=-13 gdftgrad=-13

These keywords can be set by choosing Fine from the Grid density option menu in the Theory tab of the Jaguar panel. If there are diffuse functions in your basis set, you can also try removing them.

If the geometry optimization includes solvation with the PBF solvation model, use the isolvg=2 keyword to select the most accurate available gradients. However, if convergence is still not achieved, try isolvg=1 or isolvg=0.

Keywords: Jaguar, optimize

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