I am investigating disulfide radicals of the type in Hall et al (2014) doi:10.1021/ja500087m, and I am having trouble rationalizing the results I am getting in the optimizations using Gaussian. Obviously the lowest energy is found when the charge is symmetrically distributed, but I want to investigate the geometry and energy is the charge is localized on one sulfur. If that doesn't seem to make sense chemically, trust me I know, I'm working a hunch.
I have run a CASSCF calculation but the calculation still determines the symmetrical distribution to be better and gives that result. I have tried making one of the sulfurs a separate charged fragment and the initial guess gives me a good result, but once I run the optimization it all blends.
Is there any way to get the software to give the lowest-energy-possible-if-this-one-condition-is-met?
Thanks in advance for any ideas!
Dear Max, you may try Constrained DFT in the case of charge localized in one fragment. Let's say we have complex A / A, with C-DFT you can optimize A / A+.
On the other hand, charge separation is different, let's say A+ / A-
In this case, I used to move a molecular orbital from one fragment to the other one, thus creating a hole (A+) in one fragment and an electron in the other (A-).
Hope this is useful.
Best, Pablo
PS: Sorry Gaussian does not have C-DFT as far as I know. To move orbitals, I used guess=read,alter.
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