Molecular structure refinement by direct fitting of atomic coordinates to experimental ESR spectra

► Atomic coordinates of radicals are fitted directly to the experimental ESR data. ► DFT and large-scale spin dynamics simulation algorithms are used at intermediate stages. ► Workarounds are suggested for the vibrational averaging problem and the local minima problem in spectral fitting. ► Good performance is demonstrated for tyrosyl radicals in ribonucleotide reductase.