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Singlet fission is a highly desired process in photovoltaic devices as it can significantly enhance photoelectric conversion efficiency. Exploitation of this process in photovoltaics is hindered by the lack of appropriate chromophores. We used mixed-reference spin-flip time-dependent density functional theory (TDDFT) to investigate five dicarbonyl anthracenes and phenanthrenes, with the purpose to design singlet fission chromophores. Two molecules were found to be promising candidates. For all the dicarbonyl molecules, the oxygen lone pair orbitals were found to be involved in the excited states that are relevant to singlet fission. Key words: singlet fission, materials design, excited states, mixed-reference spin-flip TDDFT, diradical character, dicarbonyl substitution. La fission d'excitons singulets est un processus fort souhaitable dans le domaine des dispositifs photovoltaiques, car elle permet d'augmenter significativement l'efficacite de conversion photoelectrique. Toutefois, l'exploitation de ce processus dans le domaine de la photovoltaique est freinee par l'absence de chromophores appropries. Nous avons utilise la theorie de la fonctionnelle de la densite dependante du temps (TD-DFT) a renversement de spin multireference pour etudier cinq anthracenes et phenanthrenes dicarbonyles dans le but de concevoir des chromophores se pretant a la fission d'excitons singulets. Nous avons trouve deux molecules qui semblent prometteuses. Nos resultats ont revele que, pour toutes les molecules dicarbonylees etudiees, les orbitales des doublets non Hants des atomes d'oxygene contribuent aux etats excites d'interet pour la fission d'excitons singulets. [Traduit par la Redaction] Mots-cles: fission d'excitons singulets, conception de materiaux, etats excites, TD-DFT a renversement de spin multireference, caractere biradicalaire, substitution dicarbonyle., Introduction For a single junction photovoltaic device, the photoelectric conversion efficiency is bounded by ~30%, which is called the Shockley-Queisser limit. (1) This limit can be exceeded by a phenomenon [...]

Multiple ERI (Electron Repulsion Integral) tensor contractions (METC) with several matrices are ubiquitous in quantum chemistry. In response theories, the contraction operation, rather than ERI computations, can be the major bottleneck, as its computational demands are proportional to the multiplicatively combined contributions of the number of excited states and the kernel pre-factors. This paper presents several high-performance strategies for METC. Optimal approaches involve either the data layout reformations of interim density and Fock matrices, the introduction of intermediate ERI quartet buffer, and loop-reordering optimization for a higher cache hit rate. The combined strategies remarkably improve the performance of the MRSF (mixed reference spin flip)-TDDFT (time-dependent density functional theory) by nearly 300%. The results of this study are not limited to the MRSF-TDDFT method and can be applied to other METC scenarios. [ABSTRACT FROM AUTHOR]

In the autonomous driving industry, there is a growing trend to employ long-wave infrared (LWIR)-based uncooled thermal-imaging cameras, capable of robustly collecting data even in extreme environments. Consequently, both industry and academia are actively researching contrast-enhancement techniques to improve the quality of LWIR-based thermal-imaging cameras. However, most research results only showcase experimental outcomes using mass-produced products that already incorporate contrast-enhancement techniques. Put differently, there is a lack of experimental data on contrast enhancement post-non-uniformity (NUC) and temperature compensation (TC) processes, which generate the images seen in the final products. To bridge this gap, we propose a histogram equalization (HE)-based contrast enhancement method that incorporates a region-based clipping technique. Furthermore, we present experimental results on the images obtained after applying NUC and TC processes. We simultaneously conducted visual and qualitative performance evaluations on images acquired after NUC and TC processes. In the visual evaluation, it was confirmed that the proposed method improves image clarity and contrast ratio compared to conventional HE-based methods, even in challenging driving scenarios such as tunnels. In the qualitative evaluation, the proposed method demonstrated upper-middle-class rankings in both image quality and processing speed metrics. Therefore, our proposed method proves to be effective for the essential contrast enhancement process in LWIR-based uncooled thermal-imaging cameras intended for autonomous driving platforms. [ABSTRACT FROM AUTHOR]

By applying a recently developed solution method for the Fredholm integral equation of the second kind, we obtain an expression for Green's function of the Smoluchowski equation with a reaction sink. The result is applied to obtain accurate analytical expressions for the time-dependent survival probability of a geminate reactant pair and the rate coefficient of the bulk recombination between reactants undergoing diffusive motions under strong Coulomb interactions. The effects of both repulsive and attractive interactions are considered, and the results are compared with the numerical results obtained by solving the equation for the survival probability and the nonequilibrium pair correlation function. It is shown that the solutions are accurate enough for most reasonable parameter values. [ABSTRACT FROM AUTHOR]

Symmetry-breaking charge transfer reaction of 9,9’-bianthracene is driven exclusively by the rotational fluctuation of solvents, not including the inertial component in the solvation dynamics. Torsional motion and bond shortening during the reaction were observed.

We use MRSF-TDDFT and NEVPT2 methods to design singlet fission chromophores with the building blocks of cyclic (alkyl)(amino)carbenes (CAACs). CAAC dimers with C2, C4, and p-phenylene spacers are considered. The substitutions with trifluoromethyls and fluorine atoms at the α C position are investigated. The electronegative substituents enhance the π accepting capability of the α C while maintaining it as a quaternary C atom. The phenylene-connected dimers with the two substitutions are identified as promising candidates for singlet fission chromophores. The cylindrically symmetric C2 and C4 spacers allow for substantial structural reorganizations in the S0-to-S1 and S0-to-T1 excitations. Although the two substituted dimers with the C4 spacer satisfy (or very close to satisfy) the primary thermodynamics criterion for singlet fission, the significant structural reorganizations result in high barriers so that the fission is kinetically unfavorable. [ABSTRACT FROM AUTHOR]

Previous analytic expressions for the time-dependent rate of diffusion-influenced electron-transfer between geminate ions were obtained for the case when the reaction occurs at a contact separation. By applying a recently developed solution method for the Fredholm integral equation of the second kind, we obtain an accurate analytic expression for the time-dependent electron-transfer rate with the account of the distance-dependent reactivity. We also consider the dependence of the rate on the initial separation between the geminate ions. We check the accuracy of the solution against numerical results obtained by solving the equation for the survival probability. The solution is found to be accurate enough for most reasonable parameter values. [ABSTRACT FROM AUTHOR]

Analytic energy gradients of individual singlet and triplet states with respect to nuclear coordinates are derived and implemented for the collinear mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT), which eliminates the problematic spin-contamination of SF-TDDFT. Dimensional-transformation matrices for the singlet and triplet response spaces are introduced, simplifying the subsequent derivations. These matrices enable the general forms of MRSF-TDDFT equations to be similar to those of SF-TDDFT, suggesting that the computational overhead of singlet or triplet states for MRSF-TDDFT is nearly identical to that of SF-TDDFT. In test calculations, the new MRSF-TDDFT yields quite different optimized structures and energies as compared to SF-TDDFT. These differences turned out to mainly come from the spin-contamination of SF-TDDFT, which are largely cured by MRSF-TDDFT. In addition, it was demonstrated that the clear separation of singlet states from triplets dramatically simplifies the location of minimum energy conical intersection. As a result, it is clear that the MRSF-TDDFT has advantages over SF-TDDFT in terms of both accuracy and practicality. Therefore, it can be a preferred method, which is readily applied to other "black-box" type applications, such as the minimum-energy optimization, reaction path following, and molecular dynamics simulations. [ABSTRACT FROM AUTHOR]