Analysis of large-scale multi-configuration self-consistent field wave functions by expectation values of local operators

Abstract

Articles you may be interested inThe multi-configuration self-consistent field method within a polarizable embedded framework J. Chem. Phys. 139, 044101 (2013); 10.1063/1.4811835Approximately extensive modifications of the multireference configuration interaction method: A theoretical and practical analysis Large multiconfiguration selfconsistentfield wave functions for the ozone moleculeWe have developed a method to analyze multi-configuration self-consistent field wave functions for open-shell systems, which may consist of a very large number of Slater determinants, by calculating their expectation values for ͑local͒ one-and two-particle operators in a numerically efficient way. Although the proposed formalism is fully general and applies to any operators referring to a subset of arbitrary orthogonal molecular orbitals, the local operators we use here are defined in terms of localized molecular orbitals. This choice permits to perform a chemically intuitive analysis of the local spin, population and charge fluctuation, also allowing to study electron correlation effects in chemical bonding. We present some applications for ionic and covalent systems considering four small molecules, H 2 , N 2 , H 2 O and CH 4 , as well as a binary transition metal complex, ͓Fe 2 S 6 ͔ 6Ϫ .

Quantum chemical ab initio calculations of the magnetic interaction in alkalithioferrates(III)

“…These are spinor and spatial constraints, respectively. The MOs of the ROHF state 11 B 1u are taken as starting orbitals for the CASSCF calculations, which means that the ten 3d-like orbitals build up the active space. Since these orbitals belong to the onedimensional irreps a g , a g , b 1u , b 1u , b 1g , a u , b 2u , b 3g , b 3u , and b 2g , the ferromagnetic Sϭ5 state belongs to irrep B 1u .…”

“…Therefore, we analyze the CASSCF wave functions for all six multiplet states Sϭ0,1,...,5 by calculating expectation values for local operators. This method for an analysis of MCSCF wave functions, which is based on localized molecular orbitals, has already been presented in more detailed in previous work by Mödl et al, 11 so we only give here a short summary of the concept. The MOs of all six CASSCF states are subjected to a Foster-Boys localization procedure.…”

“…For the dimer ͓Fe 2 S 6 ͔ 6Ϫ , we first present the results of the active-electron approach and discuss the local spin configurations on the Fe ions, applying a new method for the calculation of expectation values of local operators. 11 We then take dynamical correlation effects into account by means of multireference configuration interaction ͑MRCI͒ and averaged coupled-pair functional ͑ACPF͒.…”

The Photochemistry of 1,3-Butadiene Rationalized by Means of Theoretical Resonance Structures and Their Weights

“…[23] This decomposition was performed by calculating expectation values over local operators. [24] We computed for a definite Y AO m s by means of a formula which accounts for the non-orthogonality of the AO determinants. [25] A rapid process for computing such weights has been suggested and applied.…”

From Mononuclear to Dinuclear: Magnetic Properties of Transition Metal Complexes

“…Previous studies have demonstrated that CASSCF energy di↵erences usually provide a good approximation to the experimental spin state ordering but it is also demonstrated that the values of the magnetic coupling constants are normally too small [316,317]. The active space used for the study is the minimal one, with 8 electrons and 8 orbitals (Mn-3d 5 and Cr-3d 3 ).…”