[Pw_forum] Ionic forces not reducing

[giuseppe.mattioli at mlib.ism.cnr.it]

Dear Christopher
You should try to reduce conv_thr in &ELECTRONS, in order to have a
more accurate calculation of forces and stress. Try, for instance,
with conv_thr = 1.0d-9 (and with a lower mixing_beta, 0.2~0.3 or so,
if the electronic calculation does not converge).
HTH

Giuseppe

Quoting Christopher O'Brien <cjobrien at ncsu.edu>:

> 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
>
> ===================================================================
> 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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Giuseppe Mattioli
ISM-CNR, Italy