Electron localization functions obtained from X-ray constrained Hartree-Fock wavefunctions for mol­ecular crystals of ammonia, urea and alloxan

Constrained Hartree-Fock wavefunctions in the superposition of isolated molecules model have been calculated from precise X-ray diffraction data on crystals of ammonia (NH₃), urea [CO(NH₂)₂] and alloxan [(CO)₄(NH)₂]. The X-ray constrained wavefunctions have been used to derive and examine `electron localization' information, quantified by the true and approximate electron localization function (ELF), and the true and approximate Fermi hole mobility function (FHMF). The plots of the Fermi hole mobility function are the first to appear in the literature. The results are compared with corresponding isolated-molecule Hartree-Fock calculations to gauge the effect of the crystal environment on the isolated molecules. An error analysis is performed to indicate the features in the plots which are well determined from the experimental data. The results from all plots are broadly consistent, but the approximate ELF shows some artifacts relative to the true ELF.