Sixth-order many-body perturbation theory. I. Basic theory and derivation of the energy formula

✍ Scribed by Zhi He; Dieter Cremer

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 990 KB
• Volume: 59
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1996)59:1<15::aid-qua3>3.0.co;2-#

✦ Synopsis

The general expression for the sixth-order Msller-Plesset (MP6) energy, E(MP6), has been dissected in the principal part d and the renormalization part 9. Since 2 contains unlinked diagram contributions, which are canceled by corresponding terms of the principal part d, E(MP6) has been derived solely from the linked diagram terms of the principal part d. These have been identified by a simple procedure that starts by separating d into connected and disconnected cluster operator diagrams and adding terms associated with the former fully to the correlation energy. After closing all open disconnected cluster operator diagrams, one can again distinguish between connected and disconnected energy diagrams, of which only the former lead to linked diagram representations and, therefore, contributions to E(MP6). The connected diagram parts of d have been collected in four energy terms E(MP6),, E(MP6),, E(MP6),, and E(MP6),. The sum of these terms has led to an appropriate energy formula for E(MP6) in terms of first-and second-order cluster operators.