[Wien] Energy difference comparison of Win2k with GPAW calculation

[Peter Blaha]

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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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email:peter.blaha at tuwien.ac.at           
WWW:http://www.imc.tuwien.ac.at       WIEN2k:http://www.wien2k.at
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