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STOP_ON = Error|Alert
Default: STOP_ON = Error
Description: STOP_ON defines if the code should stop on errors only or also on alerts.
There are two instances, why one might want a more conservative choice when running calculations.
First, VASP will overwrite user provided input, if the input does not make sense. You may want to make sure that VASP does not continue in this case by setting the stricter STOP_ON = Alert
Secondly, VASP will continue if it encounters issues during the calculation if there is a chance that these disappear during the self consistency. However, if you are at a stage where you still explore what parameters to use, being more conservative makes the calculation fail faster so that you can try different parameters.