Dear Friends,
I have to find out the value of multiplicity for a protonated molecule. To study the effect of protonation in the geometrical parameters, I have optimized my molecule in the ground state using gaussian09 and after that I have added one hydrogen atom to each nitrogen in the molecule. In order to optimize the protonated species, what should be the multiplicity i should use?
Regards
Dr. Renjith Raveendran Pillai
Dear Renjith,
when you protonate your molecule, you do not add or remove any electrons, you just add point positive charge(s) to it, so to say. Therefore, multiplicity of protonated species will be the same as for the original molecule. However, if you add not H+ but H-atom, it would mean that you add one more electron. Thus, if the original species was singlet, then the species with H-atom added would be doublet.
Best regards,
Aleksey.
Dear Renjith,
By the addition of two proton the multiplicity will remain singlet as for the ground state geometry, as mentioned byAlesksey, and the charge will be + 2. Therefore the fourth line in the input file should be:
+2 1
Hoping this will be helpful,
Rafik
New_charge = Old_charge + 2
New_multiplicity=Old_multiplicity BUT it depends on your particular system.
If you had initially a triplet state, the new state could also be a singlet state or vice-versa.
Can you please tell if the multiplicity of a single proton in Gaussian will be 1 or 2. Proton is devoid of electrons but is itself 1/2 spin , so should te multiplicity be 3 ?
Thanks
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