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Hi
I have a monoclinic molecular crystal with C,H,O and Br. Which range of values for parameter POTIM could be more appropiate? I know that each system has its optimum value, but in your experience what values should be tested? I am optimizing the structure of the crystal with ISIF = 3, ISYM=2, EDIFFG = -0.01 and IBRION = 2. I have tested POTIM = 0.15, 0.3, 0.5 AND 0.8 but I do not find out which the best. I only run 10 cycles per value of POTIM, maybe is a very short number of cycles in order to test that parameter. What do you think? Any ideas, hints, clues ...?

there is no general rule of thumb for how to choose POTIM: it depends on the shape of the potential hypersurface of your system how large it can be chosen. Please mind that for the CG method, POTIM only influences the step width of the first step.
If you are not sure that the system converges to its global minimum, decrease POTIM (even below 0.15) and/or choose an alternative optimization algorithm.
Also, page 25 of optionic.pdf of the vasp-workshop tutorials may help if you are not sure about how to best optimize your system.