Charge Density Analysis of an Organic Ferroelectric. Croconic Acid: an Experimental and Theoretical Study

The charge density in the high density ( = 1.912 gcm(-3)) organic ferroelectric, croconic acid, was determined from low temperature (20 K) X-ray diffraction data, and DFT theoretical calculations. The high density was associated with strong intermolecular interaction energies. The spontaneous polarization is correlated with the derived molecular dipole moment (9.3 Debye). Improvements in multipole refinement protocols are described. Limitations in the multipole model with respect to heteronuclear bond properties are discussed.