[Pw_forum] Ionic forces not reducing

[Christopher O'Brien]

Below this is a super-cell of an interface of Cu2O and Ti. The problem is simply that the forc_conv_thr is not met within 100 iterations. etot_conv_thr is almost always met first (even decreasing etot_conv_thr to 1.0d-6). Typically, the force in this system decreases to ~0.01 Ry/B with a delta F on the same order of magnitude but fluctuates about this value. This means that I continually get the warning telling me to reduce the convergence threshold. Ideally I would like obtain a maximum force of ~1D-4. 
Does anyone have any suggestions? I am at a loss. 

Thanks in advance,
Chris O'Brien


title = 'Cu2O-Ti-case2' ,
calculation = 'vc-relax' ,
restart_mode = 'from_scratch' ,
wf_collect = .false. ,
outdir = './',
wfcdir = './',
pseudo_dir = '/share2/cjobrien/pseudo/',
prefix = 'Cu2OTi',
disk_io = 'low',
verbosity = 'minimal',
tstress = .true.,
tprnfor = .true.,
forc_conv_thr = 1.0d-4,
etot_conv_thr = 1.0d-5,
/
&SYSTEM
ibrav = 0,
celldm(1) = 8.1878,
nat = 14,
ntyp = 3,
ecutwfc = 30.0 ,
ecutrho = 300.0 ,
occupations = 'smearing' ,
smearing = 'mv' ,
degauss = 0.01 ,
/
&ELECTRONS 
conv_thr = 1.0d-6 ,
mixing_beta = 0.7 ,
/
&IONS
ion_dynamics = 'bfgs',
/
&CELL
cell_dynamics = 'bfgs',
press = 0.0,
cell_dofree = 'xyz',
/
CELL_PARAMETERS 
0.929429709 0.0 0.0
0.0 0.929429709 0.0
0.0 0.0 2.924945006
ATOMIC_SPECIES 
Cu   58.70000  Cu.pw91-n-van_ak.UPF
Ti   47.88000  Ti.pw91-nsp-van.UPF
O    16.00000  O.pw91-van_ak.UPF
ATOMIC_POSITIONS alat   
Cu      0       0       0
Cu      0.504691013     0.504691013     0
Cu      0.484702934     0.019988079     0.553031754
Cu      0.019988079     0.484702934     0.553031754
Cu      0.039976158     0.039976158     1.106063508
Cu      0.464714854     0.464714854     1.106063508
O       0.252345506     0.252345506     0.285738983
O       0.024221288     0.024221288     1.544049139
Ti      0.480469725     0.024221288     1.544049139
Ti      0.024221288     0.480469725     1.544049139
Ti      0.484702934     0.484702934     2.015504257
Ti      0.019988079     0.019988079     2.015504257
Ti      0.01575487      0.488936142     2.486959376
Ti      0.488936142     0.01575487      2.486959376
K_POINTS automatic
8 8 4 0 0 0

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Christopher J. O'Brien
cjobrien at ncsu.edu
https://sites.google.com/a/ncsu.edu/cjobrien/

Ph.D. Candidate
Computational Materials Group
Department of Materials Science & Engineering
North Carolina State University
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