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Natural orbital functional for correlation in polymers

Authors

  • Mario Piris,

    Corresponding author
    1. Institute of Physical and Theoretical Chemistry, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstrasse. 3, D-91058 Erlangen, Germany
    • Institute of Physical and Theoretical Chemistry, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstrasse. 3, D-91058 Erlangen, Germany
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  • Peter Otto

    1. Institute of Physical and Theoretical Chemistry, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstrasse. 3, D-91058 Erlangen, Germany
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Abstract

We extend a natural orbital functional to calculate correlation energies for periodic polymers. We generalize the proposed correlation matrix in a two-particle reduced density matrix to achieve a size-consistent functional. Because of the linearity in two-electron integrals, our functional does not behave properly for weakly interacting systems. We separate the Coulomb operator into two parts and consider only the short-range operator for the two-electron integrals in the correlation term of the energy functional. The long-range interactions will be included in the future development of the functional to consider dispersion interactions. Application is made to alternating trans-polyacetylene. The experimentally observed reduction of the Hartree–Fock lattice spacing by the inclusion of electron correlation is correctly predicted. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

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