I am working on a reaction in which there is a step involving the reaction between ch3 and ch2 . I have done this with wb97xd/6-311+g(d,p). now I want to repeat the same reaction which involves mostly open-shell species with a higher level of theory like MP2 with large basis set. i am doughtful that it is acuurate inouph for open shell species also. so should go for more accurate dft functional like b2plyp or should stick with mp2 ? Also I cannot afford CCSD(T) calculations.
I also want to ask that if the system is small like having nearly 20 atoms. is it necessary to include results from 2 levels of theory
You can try Minnesota density functional M062X. For your 2nd question there is no such rule. You have to make sure that results are reliable.
thank you debasish mandal sir for your helpful answer. Sir, I know about m062x functional. and up to my knowledge accuracy of wb97xd and of m062x is comparable. I wish to know that if I can use mp2 for open shell systems also. (with good accuracy)
Maybe some of the latest Minnesota functionals with Broken Symmetry would be better.
You can use MP2. Be careful about the spin contamination. Read the following page
http://www.ccl.net/cca/documents/dyoung/topics-orig/spin_cont.html
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