Assessing the accuracy of DFT functionals and <i>ab initio</i> methods for the description of multireference verdazyl radical crystalline interactions

Verdazyl radicals represent a class of organic compounds that are viewed as candidates for new electronic and magnetic materials. The performance of a range of density functional theory and wavefunction theory (<i>ab initio</i>) methods for the calculation of interaction energies of verdazyl radical dimers is evaluated. Reference energies are NEVPT2(14,8) interaction energies, with an active space comprised of the verdazyl π orbitals. Members of the Minnesota functional family are the top performing functionals for this purpose, namely the range-separated hybrid meta-GGA functional M11 and MN12-L, as well as the hybrid meta-GGA M06 and meta-GGA M06-L. The performance for these methods compared to a smaller 2 orbital, 2 electron active space was also explored. Effects of restricted open-shell HF, dispersion corrections and the calculation of singlet-triplet gaps was also investigated. Methods for the high throughput determination of interaction energies in verdazyl radical crystals are presented. This work aids in the development of new molecular solid based electronic components, by enabling energy frameworks of verdazyl radical systems to be calculated accurately and confidently with lower computational costs.