Apparent bug in MP3 portion of MP4 calculation


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Gets Around
I do not have a doctorate. I am not even sure that it is a bug, to be honest. I don't know if the commonly cited asymptotic complexity of MP4 is valid for the more flexible MBPT4, but I would guess that MBPT4 is more demanding. I haven't examined the MBPT4 code in detail so for all I know the bulk of the work is by necessity in the MBPT3 iterations, though it leads to some confusing results.

The only issue with MP4 that seems to for-sure be a bug is that it once worked with 2eorb, in NWChem 6.0, but hasn't worked with 2eorb since NWChem 6.1: http://nwchemgit.github.io/Special_AWCforum/st/id1755/bug%3A_2eorb_used_to_work_wi...