[Pw_forum] Problems using 'relax' with bfgs

[carlo sbraccia]

Dear Gabriele,

can you, please, send me the output (I can afford the 400KB) ?

carlo

Gabriele Sclauzero wrote:
> Dear PW-users,
> 
>     while using calculation= 'relax' together with the 'bfgs' algorithm 
> I encountered the following problem: the relaxation seems to proceed 
> correctly up to a certain point and the reached configuration seems to 
> be near the desired minimum position, but in the next bfgs steps the 
> systems flips between two configurations and the energy oscillates up 
> and down (around the supposed minimum position). At this point the 
> algorithm seems not to be able to recognize that we are going back and 
> forth and it does not find a configuration that matches the threshold I 
> require (i.e. 1.0d-3, that is the default) on the forces.
> 
> Shoudn't the algorithm be aware of this situation and do something 
> smarter than oscillating back and forth? Or maybe should I adjust any 
> parameters with values different from the default ones?
> 
> In the attachment is the graph with the energy flips: someone might say 
> that the difference is not so much, but the forces on the two atoms I 
> let move are still higher than the threshold.
> Who might desire the output file (is 400KB large) should ask me, I will 
> send it.
> Here is the input:
> -------
>   &control
>     calculation='relax',
>     restart_mode='from_scratch',
>     forc_conv_thr= 1.0d-3,
>     tprnfor= .TRUE.,
>     pseudo_dir = '/u/cm/sclauzer/Pseudo_/',
>     outdir='/local_scratch/sclauzer/tmp/',
>     prefix='COat6Ptwire',
>   /
>   &system
>     ibrav = 6,
>     celldm(1) = 18,
>     celldm(3) = 1.47398638,
>     nat= 8,
>     ntyp= 3,
>     ecutwfc = 29,
>     ecutrho = 300,
>     occupations= 'smearing',
>     smearing='methfessel-paxton',
>     degauss=0.01
>   /
>   &electrons
>     conv_thr = 1.0e-8
>     mixing_beta = 0.6
>   /
>   &ions
>     ion_dynamics= 'bfgs',
>     upscale= 10.d0,
>   /
> ATOMIC_SPECIES
> Pt  195.078  Ptsrnlcc.RRKJ3.UPF
> C  12.0107  C.pz-rrkjus.UPF
> O  15.9994  O.pz-rrkjus.UPF
> K_POINTS AUTOMATIC
> 1 1 13 0 0 1
> ATOMIC_POSITIONS ANGSTROM
> C  2.2  0.0  0.0    1 0 0
> O  3.343  0.0  0.0    1 0 0
> Pt  0.0  0.0  -7.02   0 0 0
> Pt  0.0  0.0  -4.68   0 0 0
> Pt  0.0  0.0  -2.34   0 0 0
> Pt  0.0  0.0  0   0 0 0
> Pt  0.0  0.0  2.34   0 0 0
> Pt  0.0  0.0  4.68   0 0 0
> -------
> 
> 
> Gabriele