I am working on Iron sulfur clusters, I need to perform broken-symmetry DFT using ORCA.
I need to study the low spin clusters which means that I will have clusters with
1) 1 Fe+3 and 3 Fe+2
2) 2 Fe+3 and 2 Fe+2
my question is how to write the valency in the ORCA inputfile ??
and could you provide me with an example for input file for broken symmetry for metaloproteins ?
the examples provided in the manual is really very simple I need more advanced one !
Hi, Fedaa, it is my pleasure to help, since I have some experience with this kind of system. And I'm just a PhD Student, but hoping to become a doctor very soon. ;-)
So, your system have:
* Cluster A = 3 Iron(III) interacting with 1 Iron(II) and
* Cluster B = 2 Iron(III) interacting with 1 Iron(II)
correct?
First, you have to know some information about your system:
* Do you have high spin or low spin in your structures? Because Fe(II) can be diamagnetic (with no unpaired electrons) or it can have 4 unpaired electrons. Fe(III), for instance, can have 5 or 1 unpaired electrons.
* Do you know, for example, how the Iron(III) on the Iron(III) island is coupling with each other? (so you can threat this Iron(III) island as a single spin)
If you have the EPR measurement of your structure you may have a clue here.
If you don’t know if you're dealing with a high or low spin case and what is the total spin on each “island” in your cluster you can always try to use permutations and test for every single case to get the one with lowest energy. Let me explain:
Is it possible that the Iron(III) island have all 3 irons in ferromagnetic coupling? In this case, the Fe(III) island may have ↑↑↑↑↑ + ↑↑↑↑↑ + ↑↑↑↑↑ unpaired electrons or ↑ + ↑ + ↑. Or, in the antiferromagnetic coupling: ↑↑↑↑↑ + ↑↑↑↑↑ + ↓↓↓↓↓ or ↑ + ↑ + ↓
So, for the Iron(III) island with 3 Irons in it you may have:
- High spin Iron(III) island with F coupling: Total Spin = 15 or with AF coupling = 5
- Low spin Iron(III) island with F coupling: Total Spin = 3 or with AF coupling = 1
For the Iron(II) island with 2 Irons in it it goes the same:
- High spin Iron(II) island with F coupling: Total Spin = 8
- Low spin Iron(II) island with AF coupling: Total Spin = 0
Let's give it a try the cluster A first?
3 x Fe(III) = 15 or 5 unpaired electrons + 1 x Fe(II) 4 unpaired electrons (lets say it does have a high spin here). Let me bet that you Iron(III) island is antiferromagnetically coupled, so I’m picking it with 5 unpaired electrons instead of 5.
Your input is something like this (using ORCA 4 or above) :
! TPSS def2-SVP def2/J UKS LargePrint VerySlowConv Grid7 NoFinalGrid
! GridX7 NoFinalGridX RIJCOSX KDIIS
%basis
newgto Fe "def2-TZVPP" end
end
%scf
Brokensym 5,4
MaxIter 200
end
%output
print[p_mos] true
print[p_basis] 5
end
*xyz 0 10
Your X Y Z coordinates here
*
I’m using the meta-GGA Functional because TPSS usually works well for solid state chemistry and I’m putting the basis set Def2-TZVPP only on Iron because calculations can go a lot faster with a bigger basis set only on the metals.
Hope this helps and, if I may be completely honest, there is much more to unpack here. Feel free to contact me on Skype if you have any more questions: henriquecsj is my skype user name.
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