Calculation of the 4,5-dihydro-1,3,2-dithiazolyl radical g tensor components by the coupled-perturbed Kohn-Sham hybrid density functional and configuration interaction methods: a comparative study

Abstract

The g tensor components of the 4,5-dihydro-1,3,2-dithiazolyl (H2DTA•) radical, which is a basic building block for molecular magnets and spintronic devices, is calculated by the coupled-perturbed Kohn-Sham (CPKS) hybrid density functional (HDF) and multireference configuration interaction-sum over states (MRCI-SOS) techniques. In both methods, the diagonalized g tensor principal axes are found to be aligned with the radical's inertial axes. The tensor components are in very good agreement with those determined experimentally by electron paramagnetic resonance (EPR) spectroscopy. The MRCI technique produced g tensor components that are more accurate than those obtained by the CPKS-HDF method. Nonetheless, to get reasonable MRCI results, one must include the in-plane and out-of-plane interactions in an unbiased way. The minimum reference space that satisfies these conditions is generated from a complete active space of nine electrons in six orbitals [CAS(9,6)] and contains a(1), a(2), b(1) and b(2) type orbitals. In addition, the number of roots in the MRCI-SOS g tensor expansion should include all excited states that range from 0 to 56,000 cm(-1). The most accurate results are obtained using an MRCI-SOS/CAS(13,9) calculation. These g tensor components are within the experimental accuracy range of 1000 ppm. The one- and two-electron contributions to the g tensor components are separated and individually analyzed. The very good agreement with experiment opens the door for further accurate calculations of spin Hamiltonian tensors of larger DTA• radicals.

Density functional theory and ab initio studies on hyperfine coupling constants of phosphinyl radicals

“…Computational methods have proven especially successful in the interpretation of EPR data acquired experimentally for a broad representation of radicals based on the first‐row elements . However, to date, significantly less attention has been paid to the applications of theoretical methods to the properties of radicals with an unpaired electron significantly located on the heavier atoms, even though such systems draw the significant attention of researchers . It is because the magnetic properties of heavier atom radicals are comparable to conventional metal‐based systems, which makes them candidates for future magnetic materials .…”

Electronic Effects in Organic Chemistry

“…An insight into the slow convergence of a selected Multi-Reference Møller Plesset Perturbation (MRPT) based approach [823] as a function of the underlying CAS space is provided by Mattar and Durelle using the 4,5-dihydro-1,3,2-dithiazolyl radical as a typical example [824]. The MRPT based approaches converge slowly as a function of the CAS space.…”

The world as viewed by and with unpaired electrons

“…ORCA (http://www.thch.uni-bonn.de/tc/orca/) and the commercial ADF (http://www.scm.com/Products/ADF.html) and Gaussian software (http://www.gaussian.com/) can calculate hyperfine couplings to all of the atoms in a free radical. Calculations of free radicals provide good values for both g values and hyperfine values [94–96]. Quantitative agreement with experiment requires further development of the calculational tools, especially the treatment of solvent interactions with the radicals [97–99].…”