Search results for "Lattice energy"
showing 8 items of 8 documents
Disorder in molecular crystals justified with the help of statistical mechanics: a case of two enantiomer solid solutions
2019
An elegant statistical mechanics approach has been exploited in combination with accurate quantum chemical calculations to justify the disorder in two previously reported racemic solids. Generated canonical ensembles and performed lattice energy calculations show that the disorder in the studied systems of small organic enantiomer molecules can be modelled with great accuracy. Ensemble averages fully correspond to the disordered structure models repeatedly obtained in X-ray diffraction studies. The present work not only demonstrates that disorder and its extent in molecular crystals can be theoretically calculated, but also explains from a thermodynamic point of view the origins of the rare…
A noncentrosymmetric crystal structure of a zwitterionic compound, pyridinium 5,7-dihydro-5,7-dioxo-6H-cyclopenta[b]pyridin-6-ylide, realized by weak…
2009
Abstract Crystal structures of pyridinium 1,3-dihydro-1,3-dioxo-2 H -inden-2-ylide (PI) of a zwitterionic molecule and its nitrogen substituted compounds, 4N-PI and 5N-PI, were solved with X-ray diffraction analyses. Whereas PI and 5N-PI showed centrosymmetric crystal structures, 4N-PI demonstrated a noncentrosymmetric crystal structure where all the molecules orient to almost the same direction. To elucidate the stability of such a polarized structure, we examined interatomic close contacts among the nearest neighbor molecules in the crystals and calculated intermolecular interaction energies with relation to those contacts. As a result, the noncentrosymmetric crystal structure of 4N-PI tu…
Electrochemical properties of crystallized dilithium squarate: insight from dispersion-corrected density functional theory.
2012
International audience; The stacking parameters, lattice constants, and bond lengths of solvent-free dilithium squarate (Li(2)C(4)O(4)) crystals were investigated using density functional theory with and without dispersion corrections. The shortcoming of the GGA (PBE) calculation with respect to the dispersive forces appears in the form of an overestimation of the unit cell volume up to 5.8%. The original Grimme method for dispersion corrections has been tested together with modified versions of this scheme by changing the damping function. One of the modified dispersion-corrected DFT schemes, related to a rescaling of van der Waals radii, provides significant improvements for the descripti…
Synthesis, crystal structure, optical, thermal and magnetic studies of a new organic-inorganic hybrid based on tetrachloroferrate (III)
2021
Abstract A new organic metal halide hybrid, benzyltrimethylammonium tetrachloroferrate (III), 1, ((BzMe3N)FeCl4) was synthesized by slow evaporation. The single crystal X-ray diffraction reveals that 1, crystallizes in the P-1 triclinic space group with the parameters a = 7.158 (5), b = 8.814 (8), c = 12.922 (4) A, α = 82.44 (5), β = 86.14 (4), γ = 87.13 (7)°, V = 805.7 (10) A3 and Z = 2. The structure packing exhibits a cationic and anionic layers alternation linked by means of C─H⋯Cl hydrogen interactions. The Hirshfeld surface and the lattice energy of 1 were calculated. The material purity was verified using X-ray powder diffraction and Rietveld refinements. The TG-DTA a…
Atomic scale DFT simulations of point defects in uranium nitride
2007
Atomic scale density functional calculations are used to predict the behaviour of defects in uranium mononitride (UN). Two different density functional codes (VASP and CASTEP) were employed with supercells containing from 8 to 250 atoms (providing a significant range of defect concentrations). Schottky and nitrogen Frenkel point defect formation energies, local lattice relaxations and overall lattice parameter change, as well as the defect induced electronic density redistribution, are discussed.
Comparison of the polymorphs and solvates of two analogous fungicides—a case study of the applicability of a supramolecular synthon approach in cryst…
2011
The polymorphism and solvate formation of thiophanate-ethyl (TE), a fungicidal active, were investigated by solvent crystallization and compared to a close analogue, thiophanate-methyl (TM). Four polymorphs and seven solvates of TE were found and structurally compared with the previously found two polymorphs and fourteen solvates of TM by analyzing the hydrogen bonding patterns and using fingerprint plots, packing coefficients and lattice energies. TE and TM have the same functional groups that can build identical supramolecular synthons. Despite the strong similarities, the polymorphs and solvates of the two actives show significant differences in hydrogen bonding and packing. The results …
Semiempirical Correlation between Optical Band Gap Values of Oxides and the Difference of Electronegativity of the Elements. Its Importance for a Qua…
1997
A semiempirical correlation between the optical band gap of binary oxides and the difference of electronegativity between the oxygen and metallic elements (Pauling's extraionic energy) is proposed. In the frame of the proposed correlation an estimate of the repulsive term in the total lattice energy of ionic oxides is obtained in very good agreement with the existing data. An extension of the correlation to the ternary oxides and hydroxides is proposed by using the concept of average cationic or anionic group electronegativity. The usefulness of the proposed correlation for the in situ characterization of passive films on metals and alloys by photocurrent spectroscopy is illustrated by repo…
Strategies for an accurate determination of the X(3872) energy from QCD lattice simulations
2014
We develop a method to determine accurately the binding energy of the X(3872) from lattice data for the DD* interaction. We show that, because of the small difference between the neutral and charged components of the X(3872), it is necessary to distinguish them in the energy levels of the lattice spectrum if one wishes to have a precise determination of the the binding energy of the X(3872). The analysis of the data requires the use of coupled channels. Depending on the number of levels available and the size of the box we determine the precision needed in the lattice energies to finally obtain a desired accuracy in the binding energy.