[gpaw-users] Full optimization in plane wave mode

[Vladislav Ivanistsev]

I've also experienced similar problem with grid spacing. What is the lowest
h value one can safely use. Is h=12 suitable?
Ph.D. Vladislav Ivanistsev


On Wed, Nov 7, 2012 at 1:33 PM, Jón Steinar Garðarsson Mýrdal
<jsmy at dtu.dk>wrote:

> Hi Janne
>
> When you change the shape or size of your super cell then the grid
> sampling will change and this can lead to a change in energy.
> Therefore it is important to run calculations where you perform cell
> optimization with extra small grid spacing.
> I would try lowering the value of h you are using.
>
> Mvh.
> Jón Steinar Garðarsson Mýrdal
> Ph.d Student
> DTU Energy Conversion
> -------------------------------------------
> Technical University of Denmark
> Department of Energy Conversion and Storage
> Frederiksborgvej 399
> Building 775
> 4000 Roskilde
> Direct +45 46775818
> jsmy at dtu.dk
> http://www.dtu.dk
>
> ________________________________________
> From: gpaw-users-bounces at listserv.fysik.dtu.dk [
> gpaw-users-bounces at listserv.fysik.dtu.dk] On Behalf Of Janne Hirvi [
> janne.hirvi at uef.fi]
> Sent: Wednesday, November 07, 2012 2:01 PM
> To: gpaw-users at listserv.fysik.dtu.dk
> Subject: [gpaw-users] Full optimization in plane wave mode
>
> Dear GPAW-users,
>
> I tried to perform "full" optimization (in orthogonal cell) for silica
> structure using plane wave mode.
>
> The script was something like this
>
> -----
> mixerown=Mixer(beta=0.1, nmaxold=5, weight=50.0)
> calc=GPAW(mode=PW(400), xc='PBE', kpts=(4,4,4), mixer=mixerown,
> txt=name+'.txt')
> Bulk.set_calculator(calc)
>
> ucf=UnitCellFilter(Bulk,mask=[1,1,1,0,0,0])
> relax=BFGS(ucf)
> traj=PickleTrajectory(name+'.traj','w',Bulk)
> relax.attach(traj)
> relax.run(fmax=0.03)
> ----
>
> The corresponding calculation converged (stress and forces are small), but
> the energies for each step
>
> Zero Kelvin:   -188.134359 (Step 1)
> Zero Kelvin:   -187.264322
> Zero Kelvin:   -187.394858
> Zero Kelvin:   -187.853520
> Zero Kelvin:   -187.879200
> Zero Kelvin:   -188.081472
> Zero Kelvin:   -188.048312
> Zero Kelvin:   -188.051650
> Zero Kelvin:   -188.081487
> Zero Kelvin:   -188.096408 (Step 10)
> Zero Kelvin:   -188.091418
> Zero Kelvin:   -188.113318
> Zero Kelvin:   -188.122375
> Zero Kelvin:   -188.072067
> Zero Kelvin:   -188.123096
> Zero Kelvin:   -188.125491
> Zero Kelvin:   -188.097103
> Zero Kelvin:   -188.125748
> Zero Kelvin:   -188.125478
> Zero Kelvin:   -188.130157 (Step 20)
> Zero Kelvin:   -188.146106
> Zero Kelvin:   -188.122699
> Zero Kelvin:   -188.065573
> Zero Kelvin:   -188.071948
> Zero Kelvin:   -188.033935
> Zero Kelvin:   -187.960727
> Zero Kelvin:   -187.975459
> Zero Kelvin:   -187.954870
> Zero Kelvin:   -187.941968
> Zero Kelvin:   -187.914349 (Step 30)
> Zero Kelvin:   -187.912083
> Zero Kelvin:   -187.911463
> Zero Kelvin:   -187.909650 (Step 33)
>
> behave quite strangely. The energy minimum has been reached around 20
> steps (only slightly smaller than that
> for the initial guess) and the final energy is quite notably higher.
>
> Do you know if this is related to large changes in cell dimensions when
> using plane wave mode or what might
> be the reason for this?
>
> Best regards,
>
> Janne Hirvi
>
> -----
> Janne Hirvi
> PhD (Physical Chemistry), Researcher
> University of Eastern Finland, Department of Chemistry
> P.O.Box 111, 80101 Joensuu, FINLAND
> Tel: +358 50 4422594 & +358 50 3474223
>
>
>
>
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