[QE-users] cell_dofree with BFGS relaxation

[Daniel Marchand]

Hi Paolo, Lorenzo,

Thanks so much for your attention to this matter. I believe this is likely
a bug in QE, and have made an issue post in gitlab.
https://gitlab.com/QEF/q-e/issues/108

On Tue, Apr 30, 2019 at 3:03 PM Paolo Giannozzi <p.giannozzi at gmail.com>
wrote:

> On Tue, Apr 30, 2019 at 2:50 PM Daniel Marchand <daniel.marchand at gmail.com>
> wrote:
>
>> Thanks again. So for the BFGS output, for whatever reason there is a
>> final SCF step, I"m not sure why.
>>
>
> it's explained in the message preceding the final step
>
> And yes, correct, the damped_dyanmics(n=50) ~= "BFGS"(n=14).
>>
>> However my concern is that for the "BFGS" the z component of all axis
>> changes, which for my use-case is very bad. However, for damp only the z
>> component of axis 3 (v3_z) is allowed to relax. Unfortunately, in my use
>> case (the one in the attached example) the damp method seems to converge
>> much much slower than BFGS. E.g. for the metrics that would affect my needs:
>>
>> grep -A3 CELL_PARAMETERS pw.out.bfgs <fast convergence in cell shape, but
>> we see shifts in the z-component of axis 1 & axis 2, which for my needs is
>> very bad>
>> grep -A3 CELL_PARAMETERS pw.out.damp_pr <slow convergence in cell shape,
>> but we see that the z-component of axis 1 & axis 2 are held fixed, which
>> for my needs is very good>
>>
>> Is there any way to make bfgs hold the z-component of axis 1 & 2 fixed,
>> like how we see for the damp_pr example?
>>
>> Best,
>>
>> Daniel
>>
>> On Tue, Apr 30, 2019 at 2:16 PM Lorenzo Paulatto <paulatz at gmail.com>
>> wrote:
>>
>>> there are several quircks:
>>>
>>> I see you did not specify ion_dynamics="damp" when doing damped
>>> dynamics, I'm not sure what happens of the ions in this case.
>>>
>>> The "BFGS" output you sent me is contains 14 steps of BFGS optimization,
>>> followed by one step of (damped?) molecular dynamics
>>>
>>> The damped dynamics run stops because it reaches the maximum of 50
>>> iterations (nstep=50) not because it has converged, but the cell it
>>> obtains is pretty much identical to the BFGS one
>>>
>>> hth
>>>
>>> On 30/04/2019 13:55, Daniel Marchand wrote:
>>> > Thanks, Lorenzo, for the rapid response. I have a bit of a concern
>>> w.r.t
>>> > the z-only relaxation. When I use BFGS the z component of all the axis
>>> > are allowed to relax. However, I do not want this, I want only the z
>>> > component of axis 3 (v3_z) to be moved, as per the description in the
>>> > documentation. This only seems possible with the damp algorithm. Here
>>> I
>>> > have attached sample input for both the bfgs and damp_pr algorithms
>>> >
>>> https://drive.google.com/file/d/17Bt8HHL55yG75cba6awvl8E_wo20KDYI/view?usp=sharing.
>>>
>>> > Perhaps I have one of the settings wrong?
>>> >
>>> > Best,
>>> >
>>> > Daniel
>>> >
>>> >
>>> > On Tue, Apr 30, 2019 at 1:07 PM Lorenzo Paulatto <paulatz at gmail.com
>>> > <mailto:paulatz at gmail.com>> wrote:
>>> >
>>> >      > 1) Is this still the case? When I enable this setting in my own
>>> >      > calculations (QE v6.3) I see the cell does indeed allow only
>>> >      > z-relaxation in the cell, but it does so for all the lattice
>>> >     directions
>>> >      > rather than just the a_3 lattice direction.
>>> >
>>> >     In general cell_dofree works with BFGS, but it is true that some
>>> times
>>> >     damped dynamics is more reliable.
>>> >
>>> >     I.e. I recently did some relaxations with cell_dofree="shape", as
>>> BFGS
>>> >     was not findign the minimum for some volumes, I just put
>>> >         cell_dynamics="damp-pr"
>>> >         ion_dynamics = 'damp'
>>> >     with everything default.
>>> >
>>> >     cheers
>>> >
>>> >     --
>>> >     Lorenzo Paulatto - Paris
>>> >     _______________________________________________
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>>> >
>>> >
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>>>
>>> --
>>> Lorenzo Paulatto - Paris
>>> _______________________________________________
>>> Quantum Espresso is supported by MaX (www.max-centre.eu/quantum-espresso
>>> )
>>> users mailing list users at lists.quantum-espresso.org
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>>
>> _______________________________________________
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>
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
> _______________________________________________
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