ZBRENT＆BRIONS problems: POTIM should be increased
2010-07-13 19:25阅读：
Part
ONE
When i relaxed the structure of TiO2 using IBRION = 2 and
EDIFFG = -1E-3 , some errors as following appears at the end of
some ionic steps in the log file:
' ZBRENT: increasing intervall'
' ZBRENT: bracketing found'
' ZBRENT: interpolating'
' ZBRENT: can't locate minimum, use default step'
Then i googled the message and found the following helpful
answer
(http://cms.mpi.univie.ac.at/vasp-forum/forum_viewtopic.php?3.1856)
:
' 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 suitab
le 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:quasi-Newton Method)
2) set ADDGRID=.True. in INCAR (only for vasp releases 4.4.5 and
newer) '
yes.it's right!
Part
TWO
After I modifying as above, then another message appeared:
N E
dE
d
eps ncg
rms
rms(c)
DAV: 1 -0.494411541193E+02
-0.49441E+02 -0.10469E-06
1950 0.105E-02
0.126E-03
DAV: 2 -0.494411538954E+02
0.22387E-06 -0.23223E-07
1950 0.601E-03
32 F= -.49441154E+02 E0= -.49441154E+02 d E
=0.754070E-06
BRION: g(F)= 0.000E+00 g(S)= 0.204E-08
BRIONS problems: POTIM should be increased
retain N= 1 mean eig=*****
eig: *******
the related explanation and solution is:
the asterisks *** simply indicate that the number which has to be
written (mean eig) does not fit into the format of the write
statement, which is f5.2 in that case (i.e., just 2 digits before
the comma).
Please note the 'BRIONS problems: POTIM should be increased',
which indicates that your ionic relaxation might get stuck.
-->
as the total energies are not converged yet, please follow that
instruction and increase POTIM in your INCAR file
(default=0.5)
or choose a different relaxation algorithm (IBRION)
