Are Solvent and Dispersion Effects Crucial in Olefin Polymerization DFT Calculations? Some Insights from Propylene Coordination and Insertion Reactions with Group 3 and 4 Metallocenes

International audienceThe primary insertion (or 1,2-insertion) of propylene into (C5Me5)2YCH2CH2CH(Me)2, as well as the primary and secondary (or 2,1) insertions of propylene into the activated ansa-zirconocene complex [{Ph(H)C-(3,6-tBu2Flu)(3-tBu-5-Me-C5H2)}ZrMe]+ were calculated with several DFT methods to find the most adequate methodology for the computation of metallocene-catalyzed olefin polymerization reactions. For the yttrium system, both solvent corrections and dispersion corrections are needed to determine energies of coordination and activation barriers in agreement with experimental data. Dispersion corrections were included directly via the use of specific functionals like B97D and M06 or were added as empirical corrections (GD3BJ) to the B3PW91 calculations. For the zirconocene system, the best method is a combination of B3PW91 with solvent corrections incorporated with the SMD continuum model. The dispersion corrections, included via both GD3BJ and M06, tend to overestimate the stabilization of the adducts because of the high steric bulk of the zirconocene system. The addition of dispersion corrections shifts the energy profiles toward lower values but does not affect the relative activation barriers. Implementation of entropy corrections counterbalances almost perfectly the dispersion corrections. The same observations arise from the study of the C–H activations of propylene induced by the zirconocene complex

Development of Gated Pinned Avalanche Photodiode Pixels for High-Speed Low-Light Imaging

This work explores the benefits of linear-mode avalanche photodiodes (APDs) in high-speed CMOS imaging as compared to different approaches present in literature. Analysis of APDs biased below their breakdown voltage employed in single-photon counting mode is also discussed, showing a potentially interesting alternative to existing Geiger-mode APDs. An overview of the recently presented gated pinned avalanche photodiode pixel concept is provided, as well as the first experimental results on a 8 × 16 pixel test array. Full feasibility of the proposed pixel concept is not demonstrated; however, informative data is obtained from the sensor operating under −32 V substrate bias and clearly exhibiting wavelength-dependent gain in frontside illumination. The readout of the chip designed in standard 130 nm CMOS technology shows no dependence on the high-voltage bias. Readout noise level of 15 e - rms, full well capacity of 8000 e - , and the conversion gain of 75 µV / e - are extracted from the photon-transfer measurements. The gain characteristics of the avalanche junction are characterized on separate test diodes showing a multiplication factor of 1.6 for red light in frontside illumination