[Wien] Energy difference comparison of Win2k with GPAW calculation

[Lyudmila Dobysheva]

11.05.2022 10:57, Gargee Bhattacharyya wrote:
> 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.

In fact we cannot reassure you that you did nothing wrong, but the 
difference does no seem surprising to me: these are two different 
methods with different approximations. I'd say that in GPAW the 
approximations are more rouph. GPAW uses frosen core, WIEN2k 
recalculates it; the potential in GPAW is tabulated as far as I know.

If you google GPAW and WIEN2k you'll get a lot of comparisons, for a 
quick example
https://www.nsc.liu.se/~pla/blog/2014/02/21/deltacodes/

Best wishes
Lyudmila Dobysheva
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