Topological analysis of experimental electron densities. 3. Potassium hydrogen(+)-tartrate at 15 K

A charge density study of crystalline potassium hydrogen(+)-tartrate has been carried out using high-resolution X-ray diffraction data collected at 15 K. Three refinement models based on the rigid-pseudoatom formalism were tested to examine how the data resolution and restrictions on the anisotropic displacement parameters affect the topology of the static densities. The different experimental results and those obtained by Hartree-Fock calculations were compared in terms of bond topological properties of the densities. The Laplacian distribution, especially for the polar bonds, was found highly sensitive to the resolution of the data included in the fit and to the treatment of the displacement amplitudes. The restriction of these quantities, based on the ab initio intramolecular force field and invoked via rigid-bond (link) type constraints, turned out to be very efficient in controlling thermal deconvolution and reducing bias in the experimental density.