Pixel calculations using Orca or GAUSSIAN for electron density automated within the Oscail package

Many discussions of the intermolecular interactions in crystal structures concentrate almost exclusively on an analysis of hydrogen bonding. A simple analysis of atom–atom distances is all that is required to detect and analyse hydrogen bonding. However, for typical small-molecule organic crystal structures, hydrogen-bonding interactions are often responsible for less than 50% of the crystal lattice energy. It is more difficult to analyse intermolecular interactions based on van der Waals interactions. The Pixel program can calculate and partition intermolecular energies into Coulombic, polarization, dispersion and repulsion energies, and help put crystal structure discussions onto a rational basis. This Windows PC implementation of Pixel within the Oscail package requires minimal setup and can automatically use GAUSSIAN or Orca for the calculation of electron density.

Thermophysical performances of (Sm1-xLux)3TaO7 (x = 0, 0.1, 0.3 and 0.5) ceramics

To optimize thermophysical performances, Sm3TaO7 was doped with Lu3+ and pressureless sintered at 1600 ?C. It was shown that Sm3+ is partly substituted by Lu3+ cations and the (Sm1-xLux)3TaO7 ceramics with a single pyrochlore structure are obtained.With increasing x value from 0 to 0.5, the band gap increases gradually from 4.677 to 4.880 eV. Owing to the enhanced phonon scattering caused by Lu3+ doping, the thermal conductivities at 800 ?C of the prepared samples are in the range of 0.95-1.44W?K?1?m?1. It was also confirmed that the phase transition is restrained effectively by substituting Sm3+ with Lu3+. Due to the reduction of crystal lattice energy and average electro-negativity difference, the thermal expansion coefficient (TEC) is heightened with increasing Lu content. TEC achieves the highest value (10.45 ? 10?6 K?1 at 1200 ?C) at the equal molar ratio between Sm3+ and Lu3+ cations (i.e. x = 0.5), which is much higher than those of 7YSZ and Sm2Zr2O7 ceramics.

Molecular and crystal structure, lattice energy and DFT calculations of two 2′-(nitrobenzoyloxy)acetophenone isomers

The two isomers 2′-(4-nitrobenzoyloxy)acetophenone (systematic name: 2-acetylphenyl 4-nitrobenzoate) (I) and 2′-(2-nitrobenzoyloxy)acetophenone (systematic name: 2-acetylphenyl 2-nitrobenzoate) (II), both C15H11NO5, with para and ortho positions of the nitro substituent have been crystallized and studied. It is evident that the variation in the position of the nitro group causes a significant difference in the molecular conformations: the dihedral angle between the aromatic fragments in the molecule of I is 84.80 (4)°, while that in the molecule of II is 6.12 (7)°. Diffraction analysis revealed the presence of a small amount of water in the crystal of I. DFT calculations of the molecular energy demonstrate that the ortho substituent causes a higher energy for isomer II, while crystal lattice energy calculations show that the values are almost equal for two isomers.