Question: Dear researchers, I am currently working on Fe, Mn, Ni, and Fe/Mn co-doping in Co₃O₄ for the investigation of magnetic and optical properties using Materials Studio (CASTEP DFT calculations). I am applying doping concentrations of 1%, 3%, 5%, and 7%, and would like guidance on the following key points:
I would greatly appreciate any detailed suggestions, especially from those who have worked on spinel structures or similar doping studies.
Thank you in advance for your support and guidance.
Hello Numan Abbas
1 - You can build a supercell using softwares like VESTA, from which you can find any tutorials on youtube. You must remove the symmetry of the system so you can replace atoms individually. But the most important is to maintain the proportions of atoms. If I am not mistaken, there are 24 cobalt atoms in this unit cell. If you replace one of these copper for a Fe atom, you have 1/24 atoms replaced. So a 2x2x1 supercell would have 96 atoms of cobalt, and so you could replace 1 atom, and the proportion is almost 1%.
To determine what is the preferential site, I suggest you try to run the calculation and check the energies. For experimental test I think XPS is a good guess.
Best regards,
Dr. Ricardo Tadeu.
if we use 2*2*1 supercell so 96 co atoms and we have to replace each co atom by dopant. so we to make separate calculation for octa and tetra site like 1/32 and 1/64 or we have to do 1/96 is also ok. we can replace 1/96 and can say on behalf to literature that doping is done on octa or tetra or we have to create supercell for octa and tetra spearate and then make a comparison?
I think you can create a 2x2x1 supercell of the unit cell of the usual structure. When you want to do 1% doping, I don't assume 1 of 100 octa sites, I assume 1 of 100 cobalt atoms. If the atoms were in the same symmetric site, there wouldn't be difference from which you replace, but you can see there are 3 different sites of cobalt. I wouldn't care for the proportion of octa and tetra, but I would study different possibilities of doping, one for each symmetric site.
Ricardo Tadeu Maia if we create 22x1 supercell we get 96 Co atoms total. so for doping we replace 96 Co atoms for example 1/96x100= 1.04% which is closet to 1%. but the main issue is the octa and tetra sites who we will conform this the doping preferred which site. because if we do doping on both octa and tetra site separately it will take alot of time. is there any other way to conform we directly confrom site.
Numan Abbas yes, these calculations will take time. As much as you increase supercell size, the more it takes. I supposed you wanted to study these dopings separately, because you would study the energy of the dopant in each site. If you do 1% for octa sites and 1% in tetra at same cell, you would have to make 200 atoms of cobalt and your supercell would be 4x4x1. From my experience, I guess that there would take less time if you did two systems with 100 cobalt atoms than a single system with 200. Or am I mistaken? Well, I am just trying to get a reasonable calculation for you, but I have never completed a study like this, I just know how to construct the input and set the calculation. You must discuss with your collaborators what is the correct manner to do it. But definitely it's not a fast calculation.
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