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Hi

Sometimes my calculations crash with the following message in standard output

ZBRENT: fatal internal in brackting
system-shutdown; contact gK immediately

The calculations run perfectly fine for sometime ans then suddenly they just die with the above error.

What might be the cause of such an error ??

Thanks a lot

this message says that during geometry optimisation no reasonable next step could be found with Brent's algorithm (linear bisectioning)
please check the following
1) is the system converged already? (look at the forces in OUTCAR, especially if you use the total energy change as congvergence criterium for ionic optimisation)
2) if not: is each ionic step converged electronically ( this is needed to obtain reasonable forces)

Well, I encounter the same problem when I optimize the geometry. I set EDIFFG=-1E-2. And every SCF is converged. But in the last SCF non-local-force acting on ions is -.178E-14 0.000E+00 0.000E+00; it seems not small enough,right? I see the total drift is 0.000063 -0.000007 -0.000005.
I don't know whether the optimization is OK ended.
Or what parameter do I need to let the convergence continue?

sometimes, if the calculation is already highly converged, vasp cannot interpolate the next step to within the numerical accuracy because it simply would be so small. (this behaviour is machine-dependent). If you have used IBRION=2, it may help to switch to IBRION=1 and set ADDGRID=.true. in addition

Thx a lot.

As said by the head admin. i have solved my NEB optimization, by switching from IBRION=2 [conjugate grad.]to IBRION=1[q-N]. thnx