Polarization propagator multiconfigurational

In the multiconfigurational polarization propagator approximation, normally called multiconfigurational random phase approximation (MCRPA), the set of 

Since in MCRPA the reference wavefunction is a variational MCSCF wave-function, one can derive the MCRPA also by application of linear response theory, Section 11.2, or of the quasi-energy derivative method, Section 12.3, to this MCSCF state. 

J0rgensen and J. Simons, Second Quantization-Based Methods in Quantum Chemistry, Academic Press, New York (1981) Chapter 6. 

McWeeny, Methods of Molecular Quantum Mechanics, Academic Press, London, 2nd edn (1992) Chapters 12 and 13. 

Oddershede, P. Jprgensen and D. L. Yeager, Polarization Propagator Methods in Atomic and Molecular Calculations, Comput. Phys. Rep. 2, 33-92 (1991). 

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In this substection we will shortly discuss the computational methods used for calculation of the spin-spin coupling constants. Two main approaches available are ab initio theory from Hartree-Fock (or self-consistent field SCF) technique to its correlated extensions, and density function theory (DFT), where the electron density, instead of the wave function, is the fundamental quantity. The discussion here is limited to the methods actually used for calculation of the intermolecular spin-spin coupling constants, i. e. multiconfigurational self consistent field (MCSCF) theory, coupled cluster (CC) theory and density functional theory (DFT). For example, the second order polarization propagator method (SOPPA) approach is not... 

MP) perturbation theory, linearized coupled cluster and multiconfigurational self-consistent field (MCSCF) wavefunctions are commonly employed as approximate reference states in polarization propagator approximations and will be discussed in Sections 10.3 and 10.4. 

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