[Pw_forum] problem in relaxation by using bfgs

[Huiqun Zhou]

Javad,

I got the same problem several months before. In my case, I noticed that if 
I
run my job on equal to or less than 2 processors (or CPU cores), it will be 
OK.

Another way to get rid of it is to comment out the pot and wfc 
extrapolation.
Of course, this will slow down your calculation to some extent.

I didn't try to use 'first_order', you may test this first.

Huiqun


----- Original Message ----- 
From: "Javad hashemifar" <jhashemifar at gmail.com>
To: <pw_forum at pwscf.org>
Sent: Friday, December 22, 2006 4:20 PM
Subject: [Pw_forum] problem in relaxation by using bfgs


> Dear Pwscf users
>
> I am trying to relax a tetragonal interface supercell at different
> values of vertical lattice parameter (celldm(3)). I am using
> calculation=relax and the namelist IONS is as follows:
>
> ion_dynamic = bfgs
> bfgs_ndim    = 3,
> pot_extrapolation = "second_order",
> wfc_extrapolation = "second_order",
>
> I have done this relaxation at several values of celldm(3) to find the
> ones that has minimum energy and zero stress. Let me to note that I
> can use of vc-relax calculations for this purpose because celldm(1) is
> fixed. For some values of celldm(3) every thing is OK and the system
> relax well and both etot_conv_thr and forc_conv_thr satisfies. But in
> some other values of celldm(3) the calculation stops with the
> following error:
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> from checkallsym : error #         1
> some of the original symmetry operations not satisfied
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> After more accurate consideration of the cases that have above error,
> I found that in that cases, the relaxation procedure has been done
> correctly for a few steps (2 - 3 step) and then in the last steps the
> position of atoms in x and y directions also has changed while there
> is no force in these two direction. But after that program has tried
> to symmetrize the position and change back the value of x and y
> positions as follows:
>
> ATOMIC_POSITIONS (alat)
> Ga       0.000000000   0.000000000   0.000000000
> As       0.000000000   0.502872976   0.354710310
> Cr        0.502872976   0.502872976   0.686421612
> As       0.502872976   0.000000000   1.018132914
>
>
>  SYMMETRIZED ATOMIC COORDINATES)
>
> ATOMIC_POSITIONS (alat)
> Ga       0.000000000   0.000000000   0.000000000
> As       0.000000000   0.500000000   0.350788698
> Cr        0.500000000   0.500000000   0.682500000
> As       0.500000000   0.000000000   1.014211302
>
> and then the above mentioned error occurs. It is the situation for all
> the cases that relaxation has not been completed.
> When I restarted one of this cases with damp method (instead of bfgs)
> the above error did not appear and the system relaxed correctly.
>
> I would appreciate if some body explains why by using bfgs such errors
> occurs and how I can solve that. Otherwise I should use the damp
> method for relaxation that usually needs to more steps to reach to the
> minimum energy.
>
> thanks in advance
> Javad Hashemifar
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