[Pw_forum] On tne optimization error in PbTiO3

[degironc]

In general calculated energies are a little noisy (due to insufficient 
scf accuracy and/or
insufficient accuracy in the integration of the XC functional on the FFT 
real space grid).
Moreover Energies and forces are slightly inconsistent (due to 
insufficient scf accuracy).
Hence it is pointless to pretend a convergence in the relaxation below 
this noise level.
When the history of the relaxation makes no sense the code reduce the 
size of the tipical
step and restart  the history, but if the step is so small that you are 
already digging below
the noise level this does not help.

By the way forc_conv_thr = 1.0D-5 is an extremey strict threshold.
default value is 1.0d-3 and usually is alread fine. 1.0d-4 should be 
more than
enough for any purpouse.

stefano

yukihiro_okuno at fujifilm.co.jp wrote:

>Dear PWscf Users.
>
>I'm now working the optimization of PbTiO3
>
>But in the process of calculation, my calculation
>
>stopped with an error like below
>
>   CASE: energy_new > energy_old
>
>     new trust radius        =       0.0000499856 bohr
>
>     trust_radius < trust_radius_min
>
>     resetting bfgs history
>
>
>
>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>     from bfgs : error #         1
>     bfgs history already reset at previous step
>
>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
>     stopping ...
>
>
>What is wrong and how to treat such an erro?
>
>This is my input file
>
>&control
>    calculation  = 'relax',
>    restart_mode = 'from_scratch',
>    pseudo_dir   = '/home/okuno/PWSCF/espresso-3.1.1/pseudo/',
>    outdir       = './',
>    forc_conv_thr = 1.0D-5
> /
> &system
>    ibrav=6
>    celldm(1)=7.36203352272
>    celldm(3)=1.07
>    nat=5
>    ntyp=3
>    nbnd=25
>    ecutwfc=30.0
>    occupations = 'fixed'
>    degauss=0.00
> /
> &electrons
>    conv_thr = 1e-7,
>    mixing_beta=0.3,
> /
>&IONS
> ion_dynamics='bfgs'
> bfgs_ndim=3
> pot_extrapolation = "second_order"
> wfc_extrapolation = "second_order"
>/
>ATOMIC_SPECIES
>  Pb    207.2     Pb.vdb.UPF
>  Ti    47.867    Ti.vdb.UPF
>  O     15.9994   O.vdb.UPF
>ATOMIC_POSITIONS {crystal}
>Pb       0.000000000   0.000000000   0.000000000
>Ti       0.500000000   0.500000000   0.534020000
>O        0.000000000   0.500000000   0.611230000
>O        0.500000000   0.000000000   0.611230000
>O        0.500000000   0.500000000   0.103910000
>K_POINTS {automatic}
>  4 4 4 1 1 1
>
>
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