MBPT4 = MP4

Hi,

Do I understand correctly that MBPT4 is equivalent to MP4 for the ground state?
So, can I change the code

mp2
 tight
 freeze atomic
end

task MP2 optimize

TCE
 MBPT4
 freeze atomic
end

task TCE optimize

for geometry optimization, taking into account the MP4 correlation?

10:39:11 AM PST - Wed, Feb 1st 2012
Short answer: yes. Note, TCE does only do numerical gradients. Bert Quote: Feb 1st 3:31 pm Hi, Do I understand correctly that MBPT4 is equivalent to MP4 for the ground state? So, can I change the code mp2 tight freeze atomic end task MP2 optimize to TCE MBPT4 freeze atomic end task TCE optimize for geometry optimization, taking into account the MP4 correlation?

Gets Around

9:38:51 AM PST - Wed, Dec 10th 2014
Quote: Feb 1st 3:31 pm Hi, Do I understand correctly that MBPT4 is equivalent to MP4 for the ground state? So, can I change the code mp2 tight freeze atomic end task MP2 optimize to TCE MBPT4 freeze atomic end task TCE optimize for geometry optimization, taking into account the MP4 correlation? Yes, and you can use both MP4 and MBPT4 as input keywords with TCE. If you have a closed-shells system, please use "mbpt4sdq(t)" instead, as this implementation is significantly more efficient than the default "mbpt4" one. In case you are curious, it is named this way because the implementation corresponds to solving MP4(SDQ) iteratively (without storing the quadruples amplitudes) and then adding the triples terms, (T), obtained via the CCSD(T) code. It's absolutely correct for closed-shell systems with canonical orbitals. Not sure about ROHF or UHF. Jeff