I am currently attempting to model defects in La2CuO4. In this attempt, I am looking to subsitute La3+ with Sr2+ which I have no problem with. Then to compensate the charge, I want to model hole formation in Cu2+, leading to Cu3+.
I have all the interatomic potentials from published data for the relevant ions, but I am unsure with the process to model this.
Should I input the potentials for Cu3+ – O2- in the initial potentials, rather than Cu2+ – O2-.
Or do I input another substitutional defect for Cu3+ in place of Cu2+, having both their potentials inputted initially.
I have tried both with not much success, so any help with the direction on this would be massively appreciated.
Here is my code, just considering the Sr2+ substitution with La3+:
defect opti conp
title
La2CuO4 Defect - Sr Subsitution
end
cell
5.3568 5.4058 13.1432 90 90 90
frac
La 0.00 -0.00672 0.36145
Cu 0.00 0.00000 0.00000
O 0.25 0.25000 -0.00719
O 0.00 0.03406 0.18367
space
B M A B
species
La core 3.25
La shel -0.25
Cu core 1
Cu shel 1
O core 0.389
O shel -2.389
Sr core -1.251
Sr Shel 3.251
buckingham
Cu shel O shel 294.15 0.40023 0.0 0 20
La shel O shel 1644.98 0.36196 0.0 0 20
O shel O shel 22764.3 0.1490 43.0 0 20
Sr shel O shel 959.1 0.3721 0.0 0 20
You just need to label your Cu atoms “Cu2” and “Cu3”, for example, and then you can specify separate interactions for Cu2 and Cu3 interacting with things so that the correct potential is selected for each case.
Thank you for your reponse. So I have implemented this, and modelled it as an impurity Cu2+ subbed to Cu3+. Having ran the simulation, when trying to calculate the defect energy, the output file states **** Conditions for a minimum have not been satisfied. However no lower point can be found - treat results with caution unless gradient norm is small (less than 0.1) after 23 cycles. My code for this is attached. Any possible help with this thanks.
defect opti conp
title
La2CuO4 Defect - Hole Species, Cu2+ to Cu3+
end
cell
5.3568 5.4058 13.1432 90 90 90
frac
La 0.00 -0.00672 0.36145
Cu2 0.00 0.00000 0.00000
O 0.25 0.25000 -0.00719
O 0.00 0.03406 0.18367
space
B M A B
species
La core 3.25
La shel -0.25
Cu2 core 1
Cu2 shel 1
O core 0.389
O shel -2.389
Sr core -1.251
Sr Shel 3.251
Cu3 core 1
Cu3 shel 2
buckingham
Cu2 shel O shel 294.15 0.40023 0.0 0 20
Cu3 shel O shel 583.93 0.35402 0.0 0 20
La shel O shel 1644.98 0.36196 0.0 0 20
O shel O shel 22764.3 0.1490 43.0 0 20
Sr shel O shel 959.1 0.3721 0.0 0 20
There is a mistake in your input since you haven’t given a spring constant for Cu3 (there should have been a warning message about this in your output). That said, for Cu2 you have an arbitrary large spring constant which means it’s not really a shell model & so you may as well just put Cu as core only. With this change, there is still a problem, as the energy blows up, which suggests your model for Cu3 in not good enough and needs refitting.