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 Andalucía 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 $(2\times 1)$ 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 $S^z_iS^z_j$ couplings. The ground state phase diagram of the spin-chain model is studied by exact diagonalization of finite chains up to $N=28$ 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 $(2\times 1)$ reconstructed phase to the disordered flat phase belongs to the $2D$ 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

Nil-Filing in Eswatini: Should the Revenue Administration be Concerned?

The tax-to-GDP ratio in developing countries is still remarkably low for many different reasons. One of the key factors behind poor tax collection is low tax compliance. In this paper we look at compliance with income tax in Eswatini, focusing on one particular dimension – filing of nil returns. Nil-filing represents a sizeable share of returns in many African countries. However, it is largely unexplored in the literature and disregarded by tax agencies, who are more interested in declarations yielding a positive return. For these reasons, we attempt to fill the gap by mapping nil-filing in Eswatini using anonymised administrative data provided by the Swaziland Revenue Authority (SRA). First, we show that over a period of five years about 30 per cent of corporate income tax (CIT) returns are nil every year. This translates into 45 per cent of taxpayers nil-filing in at least one year over the five-year period. Moreover, nil-filing varies a lot within categories of firms: it is much more likely to take place in certain districts and sectors in Eswatini, and is more common for small and younger firms. At the same time, persistent nil-filing is also very common. We also cross-check CIT data with value added tax (VAT) and Pay As You Earn (PAYE) data to monitor the filing behaviour of nil-filers across different tax returns, finding some extent of misreporting – probably due to evasion. After describing the results, we analyse additional qualitative data and provide recommendations for future research

Nil-Filing in Eswatini: Should the Revenue Authority be Bothered?

For many reasons, the tax to GDP ratio in developing countries is still remarkably low. One of the key factors behind poor tax collection refers to low tax compliance. In this paper, we look at compliance with income tax in Eswatini. Eswatini shares the same tax performance of other sub-Saharan African countries: the tax to GDP ratio is about 15%. However, Eswatini collects proportionally more income tax, for around half of its total revenue. In this setting, we focus on a particular dimension of compliance: filing of nil returns by companies. We make use of anonymous administrative data provided by the Eswatini Revenue Authority (SRA) and map the extent of nil filing in the country. The main goal of this study is to shed light on an often un-explored topic in the literature. This exercise also represents the first robust and comprehensive analysis of nil returns within the SRA. To the best of our knowledge, this is the first work of this type in any low-income country. Summary of ATAP Working Paper 6 by Fabrizio Santoro and Winnie Mdluli

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, Transformación y Resiliencia, Grant/Award Number: CA2/RSUE/2021-00890; Universidad Autonoma de Madri

An Analysis of Discrepancies in Taxpayers' VAT Declarations in Rwanda

This report provides a descriptive analysis of discrepancies resulting from matching different value added tax (VAT) data sources in the Rwanda Revenue Authority database. VAT returns are declared by businesses of all sizes and types, from companies to individual traders. Internal discrepancy is the gap between different data sources, namely VAT declaration and VAT annexes, for the same taxpayer. External discrepancy refers to the gap, for the same transaction, between buyer’s and seller’s reports. We summarise the extent and depth of these discrepancies, as well as any changes that have occurred since a new VAT refund claim validation procedure was introduced in January 2017, which mainly affected buyers’ reporting. While internal discrepancy does not seem to be an issue, external discrepancy is much more frequent, with just 18 per cent of our observations reporting the same VAT amount across buyers and sellers. This share rises to 40 per cent when buyers’ reports are compared to sellers’ electronic billing machine (EBM) records. The great majority of discrepancies are due to transactions not being reported at all by one of the trading partners. This analysis is purely descriptive and is meant to provide more information on these discrepancies, in view of potentially designing a further study to test possible policy measures to increase compliance on VAT using available administrative data

Teach to Comply? Evidence from a Taxpayer Education Programme in Rwanda

The role of taxpayer education in improving tax compliance has been largely unexplored in the literature. This paper starts to fill this gap by providing the first rigorous evaluation of the effectiveness of taxpayer education on knowledge, perceptions, and compliance, which took place in Rwanda. Our analysis is based on a unique dataset that combines administrative and survey data. We show that taxpayer education results in significant and large increases in knowledge, which starts from a very low level at baseline, and that it contributes to improving compliance behaviour. Our strongest result is that training new taxpayers helps bring them into the habit of filing tax declarations – an obligation many fail to comply with. In terms of policy, our results show that the benefits of taxpayer education go beyond increased revenue in the short term, and include building a habit of tax compliance

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

Essays on tax administration and tax compliance in sub-Saharan Africa

This thesis studies the determinants of tax compliance and the challenges of tax administration in a context of weak fiscal capacity and poor taxpayer attitudes, subSaharan Africa. The main research question regards the understanding of why African taxpayers evade taxes and which are the most effective strategies revenue authorities could pursue to foster voluntary compliance. The thesis contributes to the debate on tax revenue mobilisation in Africa by focusing on Rwanda and Eswatini. It stems from close research collaboration with national revenue authorities and relies on rich administrative data, uniquely combined with survey data. Also, it focuses on compliance of companies and self-employed with income tax, a crucial revenue source in both countries for which opportunities of tax evasion are more common. This thesis comprises three chapters. The first chapter evaluates the effectiveness of a tax training program on tax knowledge, perceptions and compliance. It combines pre and post-training survey data with tax returns records. I find that taxpayer education significantly improves knowledge and perceptions of complexity. I also show that the program brings taxpayers into the habit of filing returns, in a context where non-filing is widespread. The second chapter looks at the determinants of non-filing of tax returns in Eswatini. The motivation of this analysis comes from the large extent of this under-studied behavior in SSA. I combine survey data from 1,000 entrepreneurs with their 2013- 2018 income tax returns. I show that economic deterrence, compliance costs and moral factors are strongly correlated with actual filing. I also argue that tax knowledge plays a major role in explaining the decision to file. Lastly, the third chapter implements a randomized controlled trial nudging more than 20,000 income taxpayers in Eswatini and targeting non-filers, nil-filers and active taxpayers. I find that non-filers significantly respond to nudges, while nil and active filers do not. The best performing nudges build on the deterrence and facilitation paradigms. Also, negative responses from large companies are found