Reduced Scaling Electron Correlation Methods

We give a detailed description of recent developments in reduced scaling ab initio methods for treating electron correlation in atoms and molecules. Since configuration interaction (CI) is the simplest electron correlation method, it is introduced first and used as a context to describe the familiar local correlation and pseudospectral approximations. The article then goes on to discuss the application of these approximations to Møller–Plesset perturbation theories. We use the context of Møller–Plesset perturbation theories to introduce the use of integral-direct techniques in electron correlation. These techniques are of particular importance as they eliminate major storage bottlenecks and pave the way for the treatment of ever larger systems. As such, we give step-by-step descriptions of the simplest integral-direct algorithms. We discuss the particular usefulness of integral-direct methods when the local correlation approximation is employed and how the combination of these two approaches can yield linear scaling electron correlation methods. Additionally, we describe some newly developed Møller–Plesset approaches based upon the direct use of highly localized atomic orbitals (AO) that exploit the same physical concepts as in the canonical approaches. The article concludes with a description of coupled cluster (CC) methods that take advantage of the full range of techniques described in the discussions of configuration interaction and Møller–Plesset theories. To enhance the accessibility of the article, the underlying theories behind the various ab initio electron correlation methods are described briefly prior to describing the reduced scaling versions of the methods. About Wiley InterScience | About Wiley | Privacy | Terms & Conditions Copyright© 1999-2005 John Wiley & Sons, Inc. All rights reserved. Introduction http://www.mrw.interscience.wiley.com/ecc/articles/cu0024/sect1.html 1 of 2 7/27/2005 11:54 AM Reduced Scaling Electron Correlation Methods Emily A. Carter, University of California, Los Angeles, CA, USA Derek Walter, University of California, Los Angeles, CA, USA Encyclopedia of Computational Chemistry Copyright © 2004 by John Wiley & Sons, Ltd. All rights reserved. DOI: 10.1002/0470845015.cu0024 Article Online Posting Date: April 15, 2004