Multireference configuration interaction calculations of electronic g-tensors for NO2, H2O+, and CO+

Abstract

Electronic g-tensors parametrize the Zeeman splitting observed in the EPR spectra of radicals. In this work, we report g-tensor calculations for NO 2 , H 2 O ϩ , and CO ϩ at the multireference CI level. Deviations of the tensor elements ͑g-shifts͒ from the free-electron value are computed via a perturbation expansion, complete to second order in relevant Breit-Pauli terms. The g-shifts we obtain for these molecules are as follows: NO 2 : ⌬g xx ϭ3571, ⌬g yy ϭϪ10296, ⌬g zz ϭϪ537; H 2 O ϩ : ⌬g xx ϭϪ249, ⌬g yy ϭ15733, ⌬g zz ϭ4105; CO ϩ : ⌬g Ќ ϭϪ2383, ⌬g ʈ ϭϪ181 ͓all values in parts per million ͑ppm͔͒. These results are in reasonable agreement with gas phase experimental data. Larger g-shifts are typically within 20% of experiment, whereas smaller g-shifts generally differ by no more than several hundred ppm. Basis set effects and gauge dependence are examined in the case of CO ϩ . For this molecule, a good valence description is vital for achieving accurate ⌬g-values and small gauge-dependence. Polarization functions are of some use in these calculations, but diffuse functions have little effect on the gauge dependence of a cationic radical such as CO ϩ . Vibrational effects are also examined for CO ϩ . The vibrationally averaged g Ќ -shift only differs from the equilibrium value by 83 ppm.

The and states of N2+: hyperfine and nuclear quadrupole coupling constants, electric quadrupole moments, and electron-spin g-factors. A theoretical study

“…p 2 g , which have high DE and low L, resulting in weak second-order couplings. Thus, Dg k is dominated by first-order expectation values of appropriate operators [39][40][41]. Table 5 summarizes information pertaining to g-shifts at their respective R e Õs.…”

“…The g-factor calculations are carried out using perturbation theory and a Hamiltonian based on BreitPauli theory. First-order terms (expectation values) are evaluated at the ROHF level [40,41]. Contributions in second-order to Dg ?…”

Accurate predictions of the EPR parameters in planar cobalt(II) complexes by hybrid density functional theory

“…(1), the adiabatic parameter k has two extreme values 0 and 1 corresponding to Eqs. (2) and (3). But the difficulty arises when k varies between these two values.…”

“…Extraction of these informations from experimental spectra is however not always straightforward, quantum-chemical calculations are therefore needed [2]. Calculations of the g-and A-tensors within traditional ab initio approaches require sophisticated treatment of the electron correlation and large basis sets, which is computationally demanding [3]. These reasons make DFT a suitable tool for such a calculations [4,5].…”

Theoretical study on N2+, P2+, As2+, NP+, NAs+, and PAs+: Hyperfine coupling constants for , and electron-spin g-factors for and 1,22Σ+(XY+) states

“…First-order terms are expectation values (evaluated at the ROHF level [28,29]). Total second-order contributions are obtained via sum-over-states (SOS) expansions comprising in general nine 2 P states [30]. The n 2 P contribution to Dg (m 2 R + ) is proportional to (SO · L)/DE, where SO = AEm 2 R + |SO|n 2 Pae and L = AEm 2 R + |L|n 2 Pae are the matrix elements of the spin-orbit and angular momentum operators, and DE the energy separation, between the m 2 R + and n 2 P states.…”