Correlated ab Initio Spin Densities for Larger Molecules: Orbital-Optimized Spin-Component-Scaled MP2 Method

Abstract

The performance of the orbital-optimized MP2 method (OO-MP2) and its spin-component-scaled variant is investigated for the prediction of atomic and molecular hyperfine coupling constants (hfccs). The calculated hfccs are compared to experimental as well as to CCSD(T) reference results. The OO-MP2 isotropic hfccs for a series of small radicals are almost of CCSD quality but are obtained with iterative O (N⁵) effort. The dipolar hfccs are less well predicted by the OO-MP2 methods, whereas spin-component scaling improves the description of the hyperfine structure. The spin contamination in the OO-MP2 wave function is drastically reduced compared to the standard unrestricted Hartree-Fock wave function. The applicability of the OO-MP2 to fairly large systems is demonstrated for the solvated p-benzosemiquinone radical anion, where calculations with almost 2000 basis functions have been performed.

Toward Reliable Prediction of Hyperfine Coupling Constants Using Ab Initio Density Matrix Renormalization Group Method: Diatomic 2Σ and Vinyl Radicals as Test Cases

“…99 As a reference, these include the geometries employed in the previous work of Neese and colleagues. 38,47,100 The molecular structure of vinyl radical is shown Figure 1.…”

Hyperfine Coupling Constants from Internally Contracted Multireference Perturbation Theory

“…5 For instance, the methods based on single-reference manybody perturbation and coupled-cluster theories have been studied in the past few decades. [6][7][8][9][10][11][12] In general, the coupled cluster approaches provide benchmark accuracy when the wave function is well described by a single Slater determinant. The methods based on the complete active space selfconsistent field (CASSCF) and (uncontracted) multiconfiguration interaction (MRCI) methods have been reported as well.…”

Role of zero-point vibrational corrections to carbon hyperfine coupling constants in organic π radicals

“…[7][8][9][10][11][12][13][14][15][16][17][18] The lack of such analysis tools forced early investigations of EPR data to rely on rules-of-thumb or simple principles that relate the spin density to the measured hyperfine coupling constants (HFCCs). One such relation is the McConnell relation that states that the spin density ρ C on the carbon of a C-H fragment in an organic π radical is linearly dependent on the isotropic hyperfine constant of hydrogen.…”

“…One such relation is the McConnell relation that states that the spin density ρ C on the carbon of a C-H fragment in an organic π radical is linearly dependent on the isotropic hyperfine constant of hydrogen. [1][2][3] Although such relations or structure-property tools have frequently been used in the field of EPR, [4][5][6] recent advances in the quantum chemical modeling of HFCCs in organic radicals [7][8][9][10][11][12][13][14][15][16][17][18] offer an alternative way for exploring the physical origin of these constants.…”