[Wien] Energy difference comparison of Win2k with GPAW calculation

Wed May 11 19:29:11 CEST 2022

Oops, I missed the RMTs -- as almost always, Peter is right.

N.B., In this case the constraints mode should work. If you run into
problems contact Peter or me -- this mode is still a bit experimental, not
automated.

---
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi

On Wed, May 11, 2022, 12:20 PM Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:

> Well, the main explanation is quite simple: Of course you have to use
> IDENTICAL RMTs for the 2 calculations.
>
> I can see 1.97 and 2.23  for Ru and 1.61 and 1.17 for N.
>
> This is as if you would use 2 different pseudopotentials and compare the
> energies.
>
> Since the N2 forces you to use small N spheres, you have to use them
> allways. The Ru should be chosen according to the minimum distances.
> Everything between 2.0 and 2.2 is probably fine.
>
> I'd even start with RKmax=5.5, but eventually increase it to 6 or 6.5
> later to check if the total energy difference remains constant.
>
> In addition your cell is  "funny".  Why would you use such a rectangular
> cell with 20 and 10 bohr ???
>
> And, as already mentioned by L.Marks, in WIEN2k it is much more efficient
> to use slabs with inversion symmetry, which can be easily obtained by
> putting the N atoms on both sides of the slab.
>
> You probably started with a GPAW structure, but WIEN2k has very nice tools
> to make such calculations.
>
> You should first optimize the bulk Ru structure (at least the volume).
> Using the lowest energy structure you can easily create surface slabs
> with     x supercells  (to start with I'd suggest a 3x3x2 or 3x3x3
> supercell), and then put a N2 molecule by hand on both sides of the slab
> keeping inversion symmetry.
>
> run_law -fc 10; save unrelaxed; run_lapw -min;   save relaxed
>
> In the same directory, you could now
>
> i) manually move the 2 N atoms apart and do the same steps as before
>
> ii) use the "constraints" option of mixer to increase the N-N distance to
> a large (desired) value. This option even allows you to get the barrier
> height, not just the energy of the starting and final structures. It may
> need some fine-tuning of some input parameters, but when you watch the N-N
> distances (and the energies) during the run you should be able to make it.
>
> Regards
>
> Peter Blaha
> Am 11.05.2022 um 08:57 schrieb Gargee Bhattacharyya:
>
> Dear Developers,
>
> I am a new user of WIEN2k. I am using WIEN2k version 18.2 running on slurm
> cluster. I am using the following command in my slurm job script:
>
> *run_lapw -NI -ec 0.0001 -cc 0.01 >& job_stats.txt*
>
>
> I am trying to compare barrier height for N2 dissociation on the Ru (0001)
> surface. Using GPAW, previously I have optimized N2 adsorbed Ru slab with
> N-N distance 1.242 Å and 2N adsorbed Ru slab with N-N distance 2.701 Å
> using K mesh 3*6*1. I have calculated the energy difference as: *1.39 eV.*
> My question is:
>
> 1. When I am running scf calculation with the optimized structures and
> comparing the energy difference, I am not getting the same. I have used the
> same two structures and used 3*6*1 non shifted K mesh. The total energy
> difference I found was : 0.0416 Ry = *0.57 eV*
> I am using non-spin polarized calculations and using LDA exchange
> functional.
>
> The initial structure (N2 adsorbed Ru) and final structure (2N adsorbed Ru)
> are attached herewith.
>
> It would be helpful if you let me know whether I have done anything wrong
> in the calculation so that I can compare the energy difference GPAW and
> Win2k.
>
>
> Kind regards
> Gargee
>
>
>
> --
> Kind regards
> Gargee Bhattacharyya
> Postdoctoral Fellow
> Department of Physics and Astronomy
> Aarhus University
> Ny Munkegade 120
> 8000 Aarhus C
> Denmark
>
>
>
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> -----------------------------------------------------------------------
> Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
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