A linear scaling local correlation method,cluster-in-molecule(CIM)method,was developed in the last decade for large systems.The basic idea of the CIM method is that the electron correlation energy of a large system,within the M ller-Plesset perturbation theory(MP)or coupled cluster(CC)theory,can be approximately obtained from solving the corresponding MP or CC equations of various clusters.Each of such clusters consists of a subset of localized molecular orbitals(LMOs)of the target system,and can be treated independently at various theory levels.In the present article,the main idea of the CIM method is reviewed,followed by brief descriptions of some recent developments,including its multilevel extension and different ways of constructing clusters.Then,some applications for large systems are illustrated.The CIM method is shown to be an efficient and reliable method for electron correlation calculations of large systems,including biomolecules and supramolecular complexes.
