Troubleshooting Time-Dependent Density-Functional Theory for Photochemical Applications: Oxirane

The development of analytic-gradient methodology for excited states within conventional time-dependent density-functional theory (TDDFT) would seem to offer a relatively inexpensive alternative to better established quantum-chemical approaches for the modeling of photochemical reactions. However, even though TDDFT is formally exact, practical calculations involve the use of approximate functionals, in particular the TDDFT adiabatic approximation, whose use in photochemical applications must be further validated. Here, we investigate the prototypical case of the symmetric CC ring opening of oxirane. We demonstrate by direct comparison with the results of high-quality quantum Monte Carlo calculations that, far from being an approximation on TDDFT, the Tamm-Dancoff approximation (TDA) is a practical necessity for avoiding triplet instabilities and singlet near instabilities, thus helping maintain energetically reasonable excited-state potential energy surfaces during bond breaking. Other difficulties one would encounter in modeling oxirane photodynamics are pointed out but none of these is likely to prevent a qualitatively correct TDDFT/TDA description of photochemistry in this prototypical molecule.Comment: 19 pages, 17 figures, submitted to the Journal of Chemical Physic

Photocurable Polymers for Ion Selective Field Effect Transistors. 20 Years of Applications

Application of photocurable polymers for encapsulation of ion selective field effect transistors (ISFET) and for membrane formation in chemical sensitive field effect transistors (ChemFET) during the last 20 years is discussed. From a technological point of view these materials are quite interesting because they allow the use of standard photo-lithographic processes, which reduces significantly the time required for sensor encapsulation and membrane deposition and the amount of manual work required for this, all items of importance for sensor mass production. Problems associated with the application of this kind of polymers in sensors are analysed and estimation of future trends in this field of research are presented

Assessment of dressed time-dependent density-functional theory for the low-lying valence states of 28 organic chromophores

WOS:000297860500015International audienceAlmost all time-dependent density-functional theory (TDDFT) calculations of excited states make use of the adiabatic approximation, which implies a frequency-independent exchange-correlation kernel that limits applications to one-hole/ one-particle states. To remedy this problem, Maitra et al. [N. T. Maitra, F. Zhang, R. J. Cave, K. Burke, Double excitations within time-dependent density functional theory linear response theory, J. Chem. Phys. 120 (2004) 5932] proposed dressed TDDFT (D-TDDFT), which includes explicit two-hole/two-particle states by adding a frequency-dependent term to adiabatic TDDFT. This paper offers the first extensive test of D-TDDFT, and its ability to represent excitation energies in a general fashion. We present D-TDDFT excited states for 28 chromophores and compare them with the benchmark results of Schreiber et al. [M. Schreiber, M. R. Silva-Junior, S. P. A. Sauer, W. Thiel, Benchmarks for electronically excited states: CASPT2, CC2, CCSD, and CC3, J. Chem. Phys. 128 (2008) 134110]. We find the choice of functional used for the A-TDDFT step to be critical for positioning the 1h1p states with respect to the 2h2p states. We observe that D-TDDFT without HF exchange increases the error in excitations already underestimated by A-TDDFT. This problem is largely remedied by implementation of D-TDDFT including Hartree-Fock exchange. (C) 2011 Elsevier B. V. All rights reserved

Excited-state spin-contamination in time-dependent density-functional theory for molecules with open-shell ground states

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Modélisation physique, chimique et biologique pour la radiothérapie améliorée par les nanoparticules à fort-Z : vers une meilleure compréhension de l’effet radiosensibilisant

International audienceL’enjeu majeur de la radiothérapie est de concentrer la dose d’irradiation dans les cellules cancéreuses tout en épargnant au mieux les cellules saines. Parmi les stratégies envisagées, l’utilisation de radiosensibilisants vise à amplifier les effets destructeurs de dose dans la tumeur. Les nanoparticules (NPs) de métaux lourds tels que l’or, ont montré des propriétés radiosensibilisantes et ont des résultats prometteurs. Si leur effet est connu depuis une vingtaine d’années, l’origine de ce phénomène est encore mal comprise et peu quantifiée.La littérature suggère que, interagissant avec les NPs, les radiations génèreraient un effet physique appelé cascade Auger. Cet effet aurait pour conséquence de déposer davantage de dose localement, amplifiant les dommages cellulaires critiques par cassure directe de molécules sensibles (ADN) ou par boost de radicaux libres. Ces effets sont produits à des échelles nanométriques et dans des temps extrêmement courts (à partir de 10-18 seconde) mais ont des conséquences à échelle du patient. Parce que ce phénomène n’est pas observable, l’outil de simulation est indispensable pour mieux comprendre les processus initiaux.Notre objectif est dans un premier temps de développer une simulation permettant de calculer les distributions spatiales de dose et de radicaux libres autour des NPs et de quantifier le boost induit. Dans un second temps, nous allons injecter ces résultats dans le modèle NanOx, développé dans le cadre de l’optimisation de soin par hadronthérapie, pour traduire ces effets en termes d’augmentation de dose biologique et de mort cellulaire.Ces deux étapes feront l’objet d’une confrontation avec des données expérimentales pour évaluer la qualité des modèles et de la pertinence des scénarios proposés dans la littérature. L’objectif final serait de guider le développement des NPs et si possible d’aider à la planification clinique de traitements radiothérapeutiques basés sur les NPs

Physical, chemical and biological modelling of the radiosensitizing effect of high-Z nanoparticles

International audienceBackground: In radiotherapy, the use of radiosensitizers aims at amplifying the destructive effects of the dose in the tumor. High-Z nanoparticles have shown promising radiosensitizing properties that may originate from early physical and chemical mechanisms. A local amplification of the energy deposition inside nanotargets such as DNA, in addition to a boost of free radicals could be responsible for an increase of cell death. While it has been studied for over a decade, the understanding of such effects remains under investigation.Goal: As experimental results appear sometimes contradictory, modelling may help to better understand and quantify these early mechanisms and their impacts on cell survival.Methods: We developed Monte Carlo simulations (MCS) which track secondary electrons down to low energy both in water (meV) and gold (eV). These MCS were used to calculate the two following quantities, for an irradiated volume of water containing nanoparticles:(1) the statistical distribution of energy deposition in nanotargets, and the impact of nanoparticles on this distribution, with regard to the distance of the nanotarget to the nanoparticle surface.(2) the boost of free-radical production induced by nanoparticles, both at macro- and nanoscale.We emphasize that the time for such calculations would be prohibitive (>500 centuries on a PC) without several numerical optimizations. These two results were used in the biophysical model NanOx, originally developed to predict biological dose in hadrontherapy, to quantify the effect of nanoparticles in terms of cell death.Results: The effect of gold nanoparticles on these 3 quantities will be presented for irradiation with 20-90 keV photons, various nanoparticle sizes and concentrations.Conclusion: Nanoparticles increased the probability of energy deposition in nanotargets, especially for high energy deposition, within <200 nm around the nanoparticle. The boost of radicals was correlated with dose deposition. Both resulted in an increase of cell death