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saeed_E

Member

Registered: 2019-12-21

Posts: 292

Why do some reactions need only MP2 calculations?

Dear Tian,

There are some reactions for which corresponding TS could be located only and only at MP2 method together with correlation-consisten basis sets (at least, aug-cc-pVDZ). For such reactions employing various DFT functionals and also dispersion-corrected variants do not lead to a true TS. In other words, "DFT-functional (dispersion-corrected DFT-functional)/any basis set" should completely be ruled out in such cases. Interestingly, when literature is searched for such reactions, it is found that authors also have studied these types of reactions using MP2 method. Could you please provide a reasonable explanation for such observation? Indeed, why should these types of reactions be studied only and only using MP2 and DFT fails totally?

Sincerely,
Saeed

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,954

Website

Re: Why do some reactions need only MP2 calculations?

I don't see any evident reason that only MP2 can obtain correct result. Perhaps you didn't consider some functionals that should be considered, such as wB97XD, M06-2X. Note that due to delocalization error of some popular functionals such as B3LYP, certain TS doesn't exist if these functionals are used.

Some double-hybrid functionals are also worth to try, such as B2PLYP-D3(BJ), revDSD-PBEP86-D3(BJ), etc. If the TS located by MP2 cannot be reproduced by double-hybrid functionals, may be the TS found by MP2 actually is false.

saeed_E

Member

Registered: 2019-12-21

Posts: 292

Re: Why do some reactions need only MP2 calculations?

Dear Tian,
Many thanks for your nice, very complete, and informative comments.
Please let me state that one of such reactions is "oxidative addition" reaction for which I employed M06-2X-D3(0), wB97XD, etc. functionals but corresponding TS was not located. I also never use B3LYP functional due to its shortcoming in the producing kinetics data.
Interestingly, once MP2 is employed, the TS is correctly located. On the other hand, MP2/jul-cc-pVTZ is the method employed by author to locate such a TS whose work has been published in ChemPhysChem 2024, e202400308 (1 of 8).

In addition, I did not try double-hybrid functionals such as B2PLYP, revDSD-PBEP86, etc.to locate such TSs. I will try these functional as well.

Sincerely yours,
Saeed

Last edited by saeed_E (2025-01-01 18:39:58)

saeed_E

Member

Registered: 2019-12-21

Posts: 292

Re: Why do some reactions need only MP2 calculations?

Dear Tian,
Regarding this discussion, I sent to you an email a moment ago. Could you please have a look and let me know your valuable opinion?

Sincerely,
Saeed