2018. Elucidating the crystal structure of DL-Arginine by combined powder X-ray diffraction data analysis and periodic DFT-D calculations. AbstractAmong the 20 directly-encoded proteinogenic amino acids, arginine is one of five remaining cases for which the crystal structure of a racemic crystalline phase has not yet been reported. In this paper, the crystal structure of DL-arginine is determined by exploiting modern methods for analysis of powder X-ray diffraction data, in conjunction with periodic DFT-D calculations. The crystal structure of DL-arginine provides interesting contrasts and comparisons to that of the enantiomerically pure crystalline phase (L-arginine), which was also determined recently from powder X-ray diffraction data.