[QE-users] cell_dofree with BFGS relaxation

[Paolo Giannozzi]

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
>> _______________________________________________
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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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