Structure optimisation problem

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Structure optimisation problem

Forum: Elk Users

Creator: Marjana Lezaic

Created: 2020-01-22

Updated: 2020-02-03

Marjana Lezaic - 2020-01-22

Dear all,

I would like to perform a structure optimisation (starting from a pre-converged state) that keeps the unit cell volume fixed. So, I used tasks=3 and latvopt=2. The atoms do move around, but the unit cell shape does not change and after three optimisation steps the files STRESSMAX.OUT and STRESS_OPT.OUT are still empty. Is there another switch that I should use to get the stresses calculated?
(Just in case that it matters, I am running the version 5.2.14)

Thank you!
Marjana

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mfechner - 2020-01-22

I think

"latvopt"

has to be set to either 1/2 to perform constrained or unconstrained structural relaxation.

the default is 0, which does no lattice optimization.

best regards
michael

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mfechner - 2020-01-22

I think

"latvopt"

has to be set to either 1/2 to perform constrained or unconstrained structural relaxation.

the default is 0, which does no lattice optimization.

best regards
michael

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Marjana Lezaic - 2020-01-22

Thanks Michael, I use latvopt=2, since elk manual says "Optimisation over all symmetry-preserving strains except isotropic scaling is performed when latvopt = 2". Still, no stresses.

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mfechner - 2020-01-23

Dear Marjana,

sorry I missed your statement. Question 1 is your cell big and how are the forces after the third structural iteration? I somehow remember that lattice relaxation requieres somehow forces below a treshold but I may be wrong on this.

best regards
Michael

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Marjana Lezaic - 2020-01-23

Hi Michael (and thanks for dealing with my Elk-rookie problems),

My cell contains 8 atoms (i.e. it is on a rather small side).
This is the last line in the FORCES_OPT.OUT file: "Maximum force magnitude over all atoms (target) : 0.1246508581E-01 ( 0.1000000000E-03)". Do you suggest I should continue the calculation and wait for the forces to go under the target value? In any case, that's an easy test, I'll do it and let you know how it works. Thanks again!

Cheers,
Marjana

Last edit: Marjana Lezaic 2020-01-23

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Marjana Lezaic - 2020-02-03

Hi Michael,
You were right, the forces needed to be converged first and the stresses followed! Your advice to be patient was very wise. :-) Thanks!
Cheers,
Marjana

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