Multiconfigurational Perturbation Theory:  An Efficient Tool to Predict Magnetic Coupling Parameters in Biradicals, Molecular Complexes, and Ionic Insulators

Abstract

The performance of the complete active space second-order perturbation theory (CASPT2) to accurately predict magnetic coupling in a wide series of molecules and solid state compounds has been established. It is shown that CASPT2, based on a reference wave function that only includes the effects described by the Anderson or Hay−Thibeault−Hoffmann model, correctly reproduces all experimental trends. For a complete quantitative agreement with experiment (or with accurate results arising from the difference dedicated configuration interaction method), it is necessary to include effects that go beyond the Anderson model in the reference wave function. The CASPT2 method is computationally less demanding than CI based methods and, hence, allows us to extend the study of magnetic coupling parameters to larger molecules or systems with elevated spin moments. Moreover, CASPT2 provides a reliable and accurate alternative to density functional based methods that require the use of a broken symmetry approach.

Spin Symmetry Requirements in Density Functional Theory: The Proper Way to Predict Magnetic Coupling Constants in Molecules and Solids

“…The latter is representative of High-T c superconductor parent compound and also is used as an example of a system in condensed phase. These systems are especially well suited for this kind of study since they were also chosen to test the performance of multireference second order perturbation methods [82]. Tables 1 and 2 report the energy difference between the electronic states related to the magnetic order.…”

“…Experimental results are discussed in Refs. [4,82]. For the DFT calculations, Yes stands for the REKS/ROKS results whereas No stands for the unprojected broken symmetry results related to the Heisenberg J parameter.…”

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

“…Many calculations have shown the performance of DDCI estimates of the magnetic coupling. [20][21][22][23][24][25][26][27][28][29][30][31][32] The results reported in Table I show that the J values obtained at CAS+ S and DDCI2 levels are far from experimental ones, which suggest that an important part of the effects is missed. It is therefore concluded that 2h-1p and 1h-2p configurations bring from 30% to 50% of magnetic coupling.…”

“…So far, the DDCI approach has been extensively employed in the evaluation of J in molecular and solid state magnetic materials with a remarkable good agreement with experiment. [20][21][22][23][24][25][26][27][28][29][30][31][32] Some years ago we took benefit of this methodology to analyze in depth the physical contributions to the magnetic coupling on a series of binuclear Cu ͑II͒ complexes. 33 The use of the DDCI strategy allows not only to obtain quite accurate J values but also to analyze the various physical effects by generating CI spaces of increasing lengths that include different types of determinants.…”

[Mo2(CN)11]:5- A Detailed Description of Ligand-Field Spectra and Magnetic Properties by First-Principles Calculations

“…10 9,[12][13][14] The calculations on compounds II and III have been performed by employing a minimal active space for the expansion of the zeroth-order CASSCF wave function. It comprises the five 4d molybdenum orbitals among which the three valence electrons are distributed: CAS (3,5).…”