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An automated computational strategy is devised for the ab initio determination of the full fourth-rank piezo-optic tensor of crystals belonging to any space group of symmetry. Elastic stiffness and compliance constants are obtained as numerical first derivatives of analytical energy gradients with respect to the strain and photo-elastic constants as numerical derivatives of analytical dielectric tensor components, which are in turn computed through a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach, with respect to the strain. Both point and translation symmetries are exploited at all steps of the calculation, within the framework of periodic boundary conditions. The scheme is applied to the determination of the full set of ten symmetry-independent piezo-optic constants of calcium tungstate CaWO4, which have recently been experimentally reconstructed. Present calculations unambiguously determine the absolute sign (positive) of the π61 constant, confirm the reliability of 6 out of 10 experimentally determined constants and provide new, more accurate values for the remaining 4 constants. [ABSTRACT FROM AUTHOR]

The crystal structure of the title compound {systematic name: (S)-(+)-N-[1-(2-chloro-phen-yl)-2-oxocyclo-hexyl]meth-anam-in-ium chloride}, C(13)H(17)ClNO(+)·Cl(-), was determined at 90 (2) K. The (S)-(+)-ketamine hydro-chloride salt is a well known anesthetic compound and is dramatically more potent than its R isomer. In the title compound, the cyclo-hexa-none ring adopts a chair conformation with the oxo group in the equatorial orientation. The methyl-amino and 2-chloro-phenyl groups at the 2-position have an equatorial and an axial orientation, respectively. The packing of ions is stabilized by an infinite one-dimensional ⋯Cl⋯H-N-H⋯Cl⋯ hydrogen-bonding network, involving NH(2) (+) groups as donors and chloride anions as acceptors.

The redetermined structure of 1,3,5-trinitro-1,3,5-triaza-cyclo-hexane, C(3)H(6)N(6)O(6), at 90 (2) K has ortho-rhom-bic (Pbca) symmetry. It is of inter-est with respect to energetic compounds. The structure was originally investigated through X-ray diffraction by Hultgren [(1936). J. Chem. Phys.4, 84]. Later X-ray investigations were completed by McCrone [(1950). Anal. Chem.22, 954-955] and Harris, Reed & Gluyas [(1959). AFOSR-TR-59-165 Ohio State University Research Foundation, Columbus, Ohio, USA]. A single-crystal neutron diffraction study was performed by Choi & Prince [(1972). Acta Cryst. B28, 2857-2862] to ascertain the H-atom positions, which had not been defined by the earlier X-ray diffraction studies. All previous studies were performed at or near room temperature. The structure provided is the α polymorph of the title compound. The ring atoms are arranged in the chair conformation with two nitro groups occupying pseudo-equatorial positions and the remaining nitro group is axial. The crystal packing is stabilized by close intramolecular interactions from one H atom in each methylene group to O atoms of adjacent nitro groups, ranging from 2.251 to 2.593 Å.

THE TITLE CRYSTAL STRUCTURE (SYSTEMATIC NAME: N-methyl-1-phenyl-propan-2-aminium chloride), C(10)H(16)N(+)·Cl(-), was orginally determined by Simon, Bocskei & Torok [Acta Pharm. Hung. (1992). 62, 225-230] and Yao, Kan & Wang [Huaxue Shijie (1999). 40, 568-570] at room temperature but no atomic coordinates are available for these determinations. The mol-ecule has inter-est with respect to biological activity. In the crystal structure, inter-molecular N-H⋯Cl hydrogen bonds form one-dimensional chains.

Measurements of the Stark effect on the rotationally resolved S(1)<--S(0) fluorescence excitation spectrum of aniline are reported, providing quantitative information about the degree of charge transfer in the electronic transition. We find that mu(a)(S(1)) = 2.801 +/- 0.007 D, a value that is approximately 150% larger than the ground state, mu(a)(S(0)) = 1.129 +/- 0.005 D. The enhanced value of the dipole moment in the S(1) state is attributed to more efficient electron donation by the quasi-planar amino group to the aromatic ring.