My Community

Hi,
I relaxed a molecular system with 39 atoms, using ISMEAR = 0, SIGMA = 0.02, IBRION = 2, POTIM = 0.5.
Then I found some messages like
" ZBRENT: increasing intervall"
" ZBRENT: bracketing found"
" ZBRENT: interpolating"
" ZBRENT: can't locate minimum, use default step"
at the end of some ionic steps in the log file.

Could anyone tell me what these messages mean?
Thank you in advance.

Sinderely,
Kertick

ZBRENT is an algorithm search for a root of a function by Brent's method: Numerical recipies, Section 9.3
The problem in your case might be that the Conjugate Gradient algorithm (IBRION=2) is not suitable for very small corrections of the atomic positions if your system has almost reached equilibrium (please have a look at XDATCAR to check the size of the relaxation steps done before the ZBRENT warnings show up). Usually it is sufficient to converge a system up to maximum remaining forces of about 0.01eV/A (EDIFFG=-0.01).
please try one of the following:
1) choose a different algorithm for ionic optimization (IBRION=1)
2) set ADDGRID=.True. in INCAR (only for vasp releases 4.4.5 and newer)

ADDGRID=.True. dosn't work.

ADDGRID=.True. dosn't work.