Modified coupled-pair formalism

There are other techniques for introducing electron-correlation effects such as the coupled-cluster method (Bartlett 1989, Paldus and Cizek 1989). The coupled-electron pair formalism (CPF) (Arhlichs 1985), modified coupled-pair formalism (MCPF) and more recently averaged coupled pair formalism (ACPF) have been used (see, e.g., the papers of Bauschlicher and Langhoff 1989, 1991). The coupled-cluster methods have been mostly used for lighter molecules and have not yet been used for molecules containing lanthanides or actinides. However, the MCPF method has been used for La-containing species by Bauschlicher and co-workers. 

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