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I am about to do some research in computational chemistry, however, I do not understand one method: What is the difference between second order and third order, etc, Møller-Plesset perturbation theory? I understand that MP theories include electron correlation in comparison to Hartree-Fock and how CCSD(T) can model the dispersion forces between atoms even better, but I cannot get a grasp on the difference between MP2, MP3, MP4 etc.

Also, why would I choose to use MP3 over MP2? Especially when they can be divergent, so surely I could end up with huge discrepancies in my results?

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  • $\begingroup$ I do not understand what the issue is? This is not a homework question, can someone please clarify how it needs to be changed? $\endgroup$ Jan 24, 2022 at 18:13
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    $\begingroup$ Typically, questions should include some background about what you have done to try to solve the problem and what you already understand. It helps users craft more specific answers rather than, say, having to explain the concept of perturbation theory from scratch when you already know all that. $\endgroup$
    – Tyberius
    Jan 24, 2022 at 18:43
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    $\begingroup$ Ok, that is much appreciated; I will try to improve the question. $\endgroup$ Jan 24, 2022 at 18:48
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    $\begingroup$ Chemistry.se has a resources page including some entries point to references about computational chemistry. Jan Jensen's http://molecularmodelingbasics.blogspot.com/ may be an other entry, too. If you have a specific computation in mind, sibling mattermodelling.se may offer an audience more suitable than chemistry.se. $\endgroup$
    – Buttonwood
    Jan 24, 2022 at 21:22
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    $\begingroup$ This is a very basic question, which is answered in many of the computational chemistry textbooks. Understanding the derivation of these methods is key to understand when they can be applied and when they must fail. Do the math by yourself, it really helps. Here's a sneak peek: chemistry.stackexchange.com/q/28346/4945 $\endgroup$ Jan 25, 2022 at 1:41

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