On the validity and applicability of the connected moments expansion |
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| Institution: | 2. Theoretical Chemistry Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands;3. Stratingh Institute for Chemistry, University of Groningen, Groningen, The Netherlands;4. Ghent Quantum Chemistry Group, Department of Inorganic and Physical Chemistry, Ghent University, Gent, Belgium;1. Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA;2. Department of Mechanical Engineering, Colorado School of Mines, Golden, CO 80401, USA |
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| Abstract: | The theoretical justification, and typical convergence properties, of Cioslowski's connected moments expansion for the ground-state energy of a quantum-mechanical system are considered. This size extensive expansion is an alternative to Rayleigh-Schrodinger perturbation theory, and is expected to be useful in electronic structure calculations based on many-determinant reference functions, where perturbation theory is not applicable. It is found from example molecular electronic structure calculations that, in some cases, the expansion does not converge correctly to the true energy. An im- proved expansion derived from a padé approximant, and an analysis of its validity, is presented here. |
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