[36, 37] Later on, they updated their method by first assigning PAOs to each pair domain, and using semicanonical MP2 amplitudes for each pair in the PAO basis. This union of the early PAO and PNO approaches is the basis behind the domain-based local pair natural orbital (DLPNO) family of algorithms. In the DLPNO, the pair density is first diagonalized in the PAO basis of pair ij D