[QE-users] cell_dofree with BFGS relaxation

[Lorenzo Paulatto]

I think I found a possible solution, I put a little patch in the gitlab 
tracker, I'm not sure if you get notifications.

cheers

On 4/30/19 2:49 PM, Daniel Marchand wrote:
> Thanks again. So for the BFGS output, for whatever reason there is a 
> final SCF step, I"m not sure why. 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 
> <mailto: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>
>      > <mailto: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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>     -- 
>     Lorenzo Paulatto - Paris
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-- 
Lorenzo Paulatto - Paris