what does "ZBRENT" mean?

Message

Kertick · #1 Post by **Kertick** » Tue Oct 17, 2006 4:14 am

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

#2 Post by **admin** » Wed Oct 18, 2006 2:23 pm

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)

happy · #3 Post by **happy** » Wed Apr 28, 2010 7:42 am

ADDGRID=.True. dosn't work.

happy · #4 Post by **happy** » Wed Apr 28, 2010 7:53 am

ADDGRID=.True. dosn't work.