2,802 research outputs found
Vibronic effects on electronic spectra and nonadiabatic photophysics. A quantum/classical dynamical approach.
Quantum vibronic effects have a remarkable impact on the lineshape of electronic spectra.1 They can also play an important role in the dynamics of photophysical processes like internal conversions at Conical Intersections or charge and energy transfer in multichromophoric systems.
Recent advancements allow a fair description of such effects in rigid (harmonic) molecules in gas phase.1-4 However, in biology and in material science the photoexcited chomophores are usually embedded in a solvent, possibly establishing with them specific interactions, or even in more complex and heterogeneous environments. Moreover, many systems with interesting optical properties are flexible, i.e. the optical transition triggers large-amplitude curvilinear distortions, and this challenges the applicability of harmonic approximation. Trajectory based approaches are very suitable to deal with these scenarios but they neglect quantum nuclear effects.
We are currently working with the hope to devise robust hybrid quantum/classical (QC) approaches to merge the potentialities of trajectory based methods and those of the quantum vibronic methods developed for rigid systems in gas phase or implicit solvents.1,5-6 The system is partitioned in two subsystems: a quantum core (the chromophore or just its high-frequency modes) and an environment (which can include also large amplitude motions of the system itself and is treated at a more approximate classical level) and the challenge is the reliable description of their mutual couplings. We will illustrate our recent results with a number of examples ranging from the chiro-otpical properties of flexible conjugated systems (e.g. oligothiophenes) to the nonadiabatic decay of photoexcited DNA nucleobases7 in acqueous solution. 8-12
1. F. Santoro, D. Jacquemin, WIREs Comput Mol Sci 6, 460–486, 2016
2. M. H Beck,. A Jäckle,. G. A Worth, H.-D Meyer,. Physics Report 2000, 324
3. L. S. Cederbaum, E. Gindensperger, and I. Burghardt, Phys. Rev. Lett. 94, 113003, 2005.
4. D. Picconi, F. Avila, R. Improta, A. Lami, F. Santoro, Faraday Discuss, 163, 223, 2013
5. F. Avila, R. Improta, F. Santoro, V. Barone, Phys Chem Chem Phys. 17007, 13, 2011
6. F. Avila, J. Cerezo, J. Soto, R. Improta, F. Santoro, Comp. Chem. Theor. 1040-1041, 328, 2014
7. R. Improta, E. Stendardo, F. Avila, F. Santoro, Chem. Phys. Chem. 15 3320, 2014
8. R. Improta, F. Santoro, L. Blancafort, Chem . Rev 116, 3540 2016
9. D. Padula, F. Santoro, G. Pescitelli RSC Adv. 6, 37928, 116, 3540, 2016
10. J. Cerezo, F. Avila, G. Prampolini, F. Santoro, J. Chem. Theor. Comp. 11, 5810, 2015
11. J. Cerezo, G. Mazzeo, G. Longhi, S. Abbate, F. Santoro J. Phys. Chem. Lett. 7, 4891, 2016
12. Y. Liu, J. Cerezo, N. Lin, X. Zhao, R. Improta, F. Santoro submitted to J. Phys. Chem. Lett.Universidad de Málaga. Cammous de Excelencia Internacional AndalucĂa Tech
Disordered Flat Phase in a Solid on Solid Model of Fcc(110) Surfaces and Dimer States in Quantum Spin-1/2 Chains
We present a restricted solid on solid hamiltonian for fcc (110) surfaces. It
is the simplest generalization of the exactly solvable BCSOS model which is
able to describe a missing-row reconstructed surface. We study
this model by mapping it onto a quantum spin-1/2 chain of the Heisenberg type,
with second and third neighbor couplings. The ground state phase
diagram of the spin-chain model is studied by exact diagonalization of finite
chains up to sites, as well as through analytical techniques. We find
four phases in the phase diagram: two ordered phases in which the spins have a
N\'eel-type of long range order (an unreconstructed and a missing-row
reconstructed phase, in the surface language), a spin liquid phase
(representing a rough surface), and an intermediate dimer phase which breaks
translational invariance and has a doubly degenerate ground state,
corresponding to a disordered flat surface. The transition from the reconstructed phase to the disordered flat phase belongs to the Ising
universality class. A critical (preroughening) line with varying exponents
separates the unreconstructed phase from the disordered flat phase. The
possible experimental signatures of the disordered flat phase are discussed.Comment: 20 pages (10 Figures available upon request), REVTEX, SISSA PREPRINT
1/94/CM/S
What is the Role of Taxpayer Education in Africa?
This paper reviews existing initiatives on taxpayer education in Africa, an area that has been largely under-researched in the literature. We start by providing an overview of the wide variety of programmes that African revenue authorities have undertaken in this area, including both traditional training and more innovative approaches. We then ask how effective these programmes are, and what can be done to improve them in the future. We argue that more evaluation is needed in this area. We also highlight the importance of complementing technical training with broader educational content on the importance of paying taxes, fiscal exchange and transparency.Department for International DevelopmentBill and Melinda Gates Foundatio
FCclasses3: vibrationally-resolved spectra simulated at the edge of the harmonic approximation
We introduce FCclasses3, a code to carry out vibronic simulations of electronic spectra and nonradiative rates, based on the harmonic approximation. Key new features are: implementation of the full family of vertical and adiabatic harmonic models, vibrational analysis in curvilinear coordinates, extension to several electronic spectroscopies and implementation of time-dependent approaches. The use of curvilinear valence internal coordinates allows the adoption of quadratic model potential energy surfaces (PES) of the initial and final states expanded at arbitrary configurations. Moreover, the implementation of suitable projectors provides a robust framework for defining reduced-dimensionality models by sorting flexible coordinates out of the harmonic subset, so that they can then be treated at anharmonic level, or with mixed quantum classical approaches. A set of tools to facilitate input preparation and output analysis is also provided. We show the program at work in the simulation of different spectra (one and two-photon absorption, emission and resonance Raman) and internal conversion rate of a typical rigid molecule, anthracene. Then, we focus on absorption and emission spectra of a series of flexible polyphenyl molecules, highlighting the relevance of some of the newly implemented features. The code is freely available at http://www.iccom.cnr.it/en/fcclasses/Ministerio de Ciencia e Innovacion,
Grant/Award Number: PID2019-110091GB-I00;
Ministerio de Universidades, Plan de
Recuperacion, TransformaciĂłn y Resiliencia,
Grant/Award Number:
CA2/RSUE/2021-00890; Universidad
Autonoma de Madri
Variations on the Tournament Problem
In 1883, Lewis Carrol wrote a newspaper article to criticize how the second best player was determined in a tennis tournament, and to suggest how such a task could be done correctly. This article has been taken by Donald Knuth as the inspiration for efficiently determining the smallest t elements of a totally ordered set of size n using k-comparisons. In the ensuing research, optimal algorithms for some low values of k and t have been established, by Knuth and Aigner; for k = 2 and t ≤ 3, a few new bounds have been established for special values of n. Surprisingly, very little else is known on this problem, in spite of its illustrious pedigree and its relationship to other classical problems (e.g., selection and sorting with k-sorters). Enticed by the undeniable beauty of the problem, and the obvious promise of fun, we have joined the investigative quest. The purpose of this paper is to share some new results obtained so far. We are glad to report advances in two directions
CXCL16/CXCR6 axis drives microglia/macrophages phenotype in physiological conditions and plays a crucial role in glioma
Microglia are patrolling cells that sense changes in the brain microenvironment and respond acquiring distinct phenotypes that can be either beneficial or detrimental for brain homeostasis. Anti-inflammatory microglia release soluble factors that might promote brain repair; however, in glioma, anti-inflammatory microglia dampen immune response and promote a brain microenvironment that foster tumor growth and invasion. The chemokine CXCL16 is expressed in the brain, where it is neuroprotective against brain ischemia, and it has been found to be over-expressed in glioblastoma (GBM). Considering that CXCL16 specific receptor CXCR6 is diffusely expressed in the brain including in microglia cells, we wanted to investigate the role of CXCL16 in the modulation of microglia cell activity and phenotype, and in the progression of glioma. Here we report that CXCL16 drives microglia polarization toward an anti-inflammatory phenotype, also restraining microglia polarization toward an inflammatory phenotype upon LPS and IFN? stimulation. In the context of glioma, we demonstrate that CXCL16 released by tumor cells is determinant in promoting glioma associated microglia/macrophages (GAMs) modulation toward an anti-inflammatory/pro-tumor phenotype, and that cxcr6ko mice, orthotopically implanted into the brain with GL261 glioma cells,survive longer compared to wild-type mice. We also describe that CXCL16/CXCR6 signaling acts directly on mouse glioma cells, as well as human primary GBM cells, promoting tumor cell growth, migration and invasion. All together these data suggest that CXCL16 signaling could represent a good target to modulate microglia phenotype in order to restrain inflammation or to limit glioma progression
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