How we can locate a single electron spin on a particular metal center in a transition metal coordination complex by broken symmetry DFT by using ORCA?
I am not familiar with ORCA, but in general you cannot locate a particular electron on a particular atom with DFT. You tell the program how many up and how many down spins and it determines the lowest energy configuration. In some cases, you can bias a DFT method toward a local solution with an appropriate starting guess.
The only way I know to confine an electron to a region of a molecule is using Constrained DFT. This has not been implemented in all DFT codes; don't know whether it's in ORCA.
ORCA uses the BS(M,N) approach, with M and N being the number of unpaired electrons in fragments A and B. The program first calculates a higher multiplet, then a localization scheme is applyed and finally a lower spin state is enforced in a calculation with the previous as a starting point. You can find more information in the manual and in a few papers by Frank Neese.
Its same as Daniel mentioned above where you can provide BS(N,M) approach, where M and N are the number of unpaired electron on the two fragments A and B. It uses the spin flip approach to estimate the Broken symmetry solutions. For more details you just look in to the mannual.
You can use this keyword in your input.
%scf BrokenSym NA,NB
end
Your NA should be larger or equal to NB
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