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J Chem Phys. 2004 Apr 15;120(15):6841-8.

Analytic second derivatives for general coupled-cluster and configuration-interaction models.

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  • 1Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany. kallay@uni-mainz.de

Abstract

Analytic second derivatives of energy for general coupled-cluster (CC) and configuration-interaction (CI) methods have been implemented using string-based many-body algorithms. Wave functions truncated at an arbitrary excitation level are considered. The presented method is applied to the calculation of CC and CI harmonic frequencies and nuclear magnetic resonance chemical shifts up to the full CI level for some selected systems. The present benchmarks underline the importance of higher excitations in high-accuracy calculations.

(c) 2004 American Institute of Physics.

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