A second-order multi-reference quasiparticle-based perturbation theory

  • Zoltán RolikEmail author
  • Mihály Kállay
Part of the Highlights in Theoretical Chemistry book series (HITC, volume 12)


The purpose of this paper is to introduce a second- order perturbation theory derived from the mathematical framework of the quasiparticle-based multi-reference coupled-cluster approach (Rolik and Kallay in J Chem Phys 141:134112, 2014 ). The quasiparticles are introduced via a unitary transformation which allows us to represent a complete active space reference function and other elements of an orthonormal multi-reference basis in a determinant-like form. The quasiparticle creation and annihilation operators satisfy the fermion anti-commutation relations. As the consequence of the many-particle nature of the applied unitary transformation these quasiparticles are also many-particle objects, and the Hamilton operator in the quasiparticle basis contains higher than two-body terms. The definition of the new theory strictly follows the form of the single-reference many-body perturbation theory and retains several of its beneficial properties like the extensivity. The efficient implementation of the method is briefly discussed, and test results are also presented.


Multi-reference Perturbation theory Quasiparticles 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.MTA-BME “Lendület” Quantum Chemistry Research Group, Department of Physical Chemistry and Materials ScienceBudapest University of Technology and EconomicsBudapestHungary

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