when using ionmov=3, optcell=1 (Broyden-Fletcher-Goldfarb-Shanno minimization) on Copper with the pseudopotential 29-Cu.LDA.fhi the following error occurs in multiple Broyden iterations
" findmin : WARNING -
The 2nd degree equation has no positive root (choice=4).
findmin : COMMENT -
Will continue, since the new total energy is lower
than the old. Take a larger step in the same direction.
line minimization, algorithm 4"
The code continues to run, but the length never converges oscillating between about 5 and 9 Bohr (around the experimental value ~6.6).
Using a different pseduopotential .pspnc, I did not come accross this error. Using Gold instead of copper I found that this warning would occur for both pseudopotentials but after a few iterations it would disappear and the cell volume would converge.
Any idea why?
I enlcose my full input
Code: Select all
occopt 4
tsmear 0.01
acell 3*6.6
rprim 0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
optcell 1
ionmov 2
ntime 20
dilatmx 3
ecutsm .5
ntypat 1
znucl 29
natom 1
typat 1
xred
0.0 0.0 0.0
ecut 10.0
ngkpt 4 4 4
nshiftk 4
shiftk 0.5 0.5 0.5
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
nstep 25
toldfe 1.0d-6
(Note the parameters ecut, ngkpt and tsmear have not been converged; this is just an initial test)
Cheers.
P.S.
Actually using ionmov=2 seems to resolve the issue. However, I am still interested in why it occurs.