[Wien] Energy difference comparison of Win2k with GPAW calculation

Mon May 16 07:52:19 CEST 2022

Dear Sir,

Thank you for your helpful suggestions. Yes, I noticed the different RMT
used for the two calculations. However, I did not set any reduction % for
both the structures, and the initial RMT for both initial and final
structures were the same. I will make sure to use the same RMT and run the
calculations.

RKmax was set to 7, but I will try with 5.5 to 6.5.

Yes, you are right, I started with GPAW calculations and took the optimized
structures from there. These were just for checking whether I can compare
the energy difference.

Okay, I will do volume optimization with Win2k and make a supercell as
you suggested and I can run with Win2k.

Thank you,
Gargee

On Wed, 11 May 2022 at 19:29, Laurence Marks <laurence.marks at gmail.com>
wrote:

> 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
>> Phone: +43-158801165300
>> Email: peter.blaha at tuwien.ac.at
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-- 
Kind regards
Gargee Bhattacharyya
Postdoctoral Fellow
Department of Physics and Astronomy
Aarhus University
Ny Munkegade 120
8000 Aarhus C
Denmark
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