Quick Review of MPPT Energes

 

• Electron Correlation not introduced until second order (i.e. MP1 = SCF).
  
  
• Second Order Energy correction only involves doubly excited determinants coupling with the reference determinant.
• Third Order Energy correction only involves doubly excited determinants coupling with each other and the reference determinant.
• Fourth Order Energy correction involves doubly excited determinants coupling with the reference determinant as well as with singly, doubly, triply and quadruply excited determinants.