Charge density research: from inorganic and molecular materials to proteins

Abstract

International audienceThis paper intends to present applications of experimental charge density research in physics, chemistry and biology. It describes briefly most methods for modelling the charge density and calculating and analyzing derived properties (electrostatic potential, topological properties). These methods are illustrated through examples ranging from material science and coordination chemistry to biocrystallography, like the estimation of electrostatic energy in a zeolite-like material or the relation between electrostatic energy and spin density to macroscopic magnetic properties in a ferrimagnetic molecular material. The accurate structure and charge density of a coordination compound exhibiting LIESST effect is also described, together with an exemple of transferability of charge density methods to macromolecular science and protein crystallography

Interpretation of Experimental Electron Densities by Combination of the QTAMC and DFT

“…Generalizing previous experience [11][12][13][14][15][16][17][18][19] we can conclude that X-ray diffraction experiments yield a quasi-static model of electron density extrapolated to infinite resolution, which is, typically, as precise around the bond critical point as @0.05 e Å À3 . The experimental error becomes larger closer to nuclei and increases with the atomic number in the vicinity of nuclei; therefore ''internal'' atomic regions (R A 0.3 Å ) are normally excluded from consideration.…”

“…After other work [58,62,63,[66][67][68], the approach summarized above became a popular tool for determination of the energy characteristics at the bond critical points of crystalline systems [14][15][16][17][18][19][67][68][69][70][71]. It is, however, necessary to mention that the above-mentioned inability of the current multipole models to correctly describe the curvature of the experimental electron density along the bond path for shared atomic interaction influences all existing QTAMC bonding descriptors which contain the Laplacian term.…”

“…Originally, QTAMC was developed using electron density calculated from the wavefunctions. This approach is now widely used for exploration of experimental features of electron density; a thorough review of the results obtained from this type of work is available elsewhere [12][13][14][15][16][17][18][19]. Initial application of QTAMC to the experimental electron density of compounds with different types of chemical bond [6][7][8][9][10][11] showed that this function has a similar topology and the same set of critical points as quantum-mechanical r. Thus, the experimental electron density seems to be suitable for the QTAMC analysis of bonding in molecules and crystals, with electron density deduced from the wavefunctions.…”

Photo-crystallography: from the structure towards the electron density of metastable states

“…During the LS → HS LIESST transition (15K, 488 nm, 40 mW), we also followed the evolution of the diffraction patterns versus time and observed a Bragg peak splitting, which is characteristic of the growth of HS phase domains as already noticed during the thermal transition [8]. The conversion was nearly achieved within 15min [15].…”

Synergy between polymorphism, pressure, spin-crossover and temperature in [Fe(PM-BiA)2(NCS)2]: a neutron powder diffraction investigation

“…1-3 These materials are especially interesting owing to their bistability properties, which give them promising applications such as data storage elements, thermal switches, pigments or display devices. As notably shown by diffraction experiments, spin-crossover complexes can change their spin state upon the variation of a thermodynamic parameter such as temperature, 12,13 pressure, [14][15][16][17] intense magnetic field 18 or light irradiation. This electron redistribution corresponds to drastic structural variations, principally observed in the iron-coordination sphere.…”