I am trying to find the transition state (TS) using Gaussian Package. But for my system the spin multiplicity of the reactant and product is different. So, What should be the spin multiplicity of the TS? Also even if I try different spin multiplicities of the TS, it is causing problem while performing IRC calculation. Should I take the same spin multiplicities for reactant, product, and TS? Please give your suggestions.
Thank you.
Hi Megha,
the multiplicity of your ts has to be the same as your reactant. Only products may have a different multiplicity (to my experience at least.)
The IRC calculation may sometimes very difficult to perform, depending on the atoms you have. With metals I have quite often difficulties to do it. So I am using another way which helps also when the TS (or qst2, qst3) calculations do not work : it consists in calculating geometries with
a various values of a fixed coordinate, the one which is (or seems) to be involved the most in the reaction (for instance a bond elongation). Then by plotting the energies vs this coordinate, you will see the ts appearing (at the top) and you will have connected the reactants to the products.
I hope this helps
Héloïse
Héloïse Dossmann Ma'am in my case even if I am taking multiplicity of TS same as reactant and multiplicity of product is different from that of reactant, while performing IRC it is converging to the geometry of reactant and product having the same multiplicity. Is it the case that I should consider same multiplicity for reactant, product, and TS?
Yes then if it’s given by irc. Maybe you need to consider one further step to get your product with another multiplicity (ie radiative transfer or intersystem crossing. By the way what is your reaction? You cannot change the multiplicity of the product if it is a rearrangement.
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