Linear and nonlinear optical properties of a series of Ni-dithiolene derivatives

Some linear and nonlinear optical (NLO) properties of Ni(SCH)4 and several of its derivatives have been computed by employing a series of basis sets and a hierarchy of methods (e.g., HF, DFT, coupled cluster, and multiconfigurational techniques). The electronic structure of Ni(SCH)4 has been also analyzed by using CASSCF/CASPT2, ab initio valence bond, and DFT methods. In particular we discuss how the diradicaloid character (DC) of Ni(SCH)4 significantly affects its NLO properties. The quasidegeneracy of the two lowest-energy singlet states 1 mathg and 1 math1u, the clear DC nature of the former, and the very large number of low-lying states enhance the NLO properties values. These particular features are used to interpret the NLO properties of Ni(SCH)4. The DC of the considered derivatives has been estimated and correlated with the NLO properties. CASVB computations have shown that the structures with Ni(II) are the dominant ones, while those with Ni(0) and Ni(IV) have negligible weight. The weights of the four diradical structures were discussed in connection with the weight of the structures, where all the electrons are paired. Comparative discussion of the properties of Ni(SCH)4 with those of tetrathia fulvalene demonstrates the very large effect of Ni on the properties of the Ni-dithiolene derivatives. A similar remarkable effect on the NLO properties is produced by one or two methyl or C3S groups. The considered Ni-dithiolene derivatives have exceptionally large NLO properties. This feature in connection with their other physical properties makes them ideal candidates for photonic [email protected]

Structural, electronic, elastic, and piezoelectric properties of alpha-quartz and MX O4 ( M=Al, Ga, Fe; X=P, As) isomorph compounds: A DFT study

International audienceWe report the structural, electronic, elastic, and piezoelectric properties of some α-quartz SiO2 isotypes, namely, AlPO4, GaPO4, GaAsO4, and FePO4. This family of crystals is well known for its elastic and piezoelectric properties related to their MO4 and XO4 tetrahedral units, especially the M-O-X bridging angle θ and the tilt angle δ, the most distorted structures being expected to exhibit the highest piezoelectric coupling const. We have then computed the optimized structure of each MXO4 isomorph compd. to study the variation in the elastic and piezoelectric tensors with respect to θ and δ. A comparison between our results at the d.-functional theory level and the available data (theoretical and experimental ones) was made. The differences observed for the whole class of systems was discussed and a comparison with the SiO2 α-quartz behavior is made