Multi-temperature Electron Density Studies

Anharmonic motionsversusdynamic disorder at the Mg ion from the charge densities in pyrope (Mg3Al2Si3O12) crystals at 30 K: six of one, half a dozen of the other

“…A total of 7486 diffracted intensities were measured out to 2 θ = 109° [(sin θ / λ ) max = 1.14 Å –1 ] using a scintillation counter point-detector. Consolidated procedures for low-temperature high-quality data collection and reduction were adopted (Destro et al , 2000, 2004, 2005, 2010; Lo Presti et al , 2006; Lo Presti & Destro, 2008). They include: (i) a re-measurement of the strongest reflections at a lower current setting, to minimize problems associated with counter saturation effects, and (ii) measurement of selected profiles at the largest feasible scan width, to evaluate part of the scan-truncation correction (see below).…”

Molecular Dynamics Simulation of Molecular Crystals under Anisotropic Compression: Bulk and Directional Effects in Anthracene and Paracetamol

“…X-ray crystallography has given for half a century a fundamental contribution to the quantitative understanding of molecular recognition and crystal packing. For all its merits, it does however provide only a space–time average picture, a limitation that obscures entropic and vibrational effects on cohesive energies. − Dynamic information from standard X-ray diffraction experiments is confined to atomic displacement parameters (ADPs), whose interpretation is not always immediate in terms of fundamental physics. , Accounting for dynamic effects is obviously desirable in principle and also for cutting-edge applications like, for example, energy transduction and shape-changing materials . Moreover, thermal expansion coefficient and isothermal compressibility rely on a dynamic interplay among intermolecular interaction forces, often comprehensively dubbed noncovalent interactions (NCIs).…”

“…1−3 Dynamic information from standard Xray diffraction experiments is confined to atomic displacement parameters (ADPs), whose interpretation is not always immediate in terms of fundamental physics. 4,5 Accounting for dynamic effects is obviously desirable in principle and also for cutting-edge applications like, for example, energy transduction 6 and shape-changing materials. 7 Moreover, thermal expansion coefficient and isothermal compressibility rely on a dynamic interplay among intermolecular interaction forces, often comprehensively dubbed noncovalent interactions (NCIs).…”

Single N–C Bond Becomes Shorter than a Formally Double N═C Bond in a Thiazete-1,1-dioxide Crystal: An Experimental and Theoretical Study of Strong Crystal Field Effects

“…9 The ρ(r) scalar field is a quantum−mechanical observable and is accessible from both theoretical simulations and accurate single-crystal X-ray experiments at low temperature. 10 From a physical viewpoint, the true origin of localization and delocalization effects resides in the correlated motion of electrons, which is fully described by the twoelectron (pair) density and by the so-called "electron sharing indices" (ESI) 11 derived thereof. The most widely used ESI are undoubtedly the localization, λ(A,A), and delocalization, δ(A,B), indices.…”