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The reaction force profile and the electronic reaction flux concepts were explored for the herbicide alloxydim and some of its derivatives at B3LYP/6-311G(d,p) level of theory. The exploration was achieved by rotating the oxime bond which is the most reactive region of the molecule. The main objective is to understand how the rotation of this bond influences the properties of the molecule and induces an electronic reorganization. The results show that the rotation of the dihedral angle triggers alloxydim to go through three transition states. The first step of the transformation begins by the rupture of the hydrogen bond and is characterized by a pronounced structural reorganization. In the last step of the process the electronic reorganization is more important.

International audience; We present a combined experimental and theoretical study of the fragmentation of singly and doubly N-methylated glycine (sarcosine and N,N-dimethyl glycine, respectively) induced by low-energy (keV) O6+ ions. Multicoincidence mass spectrometry techniques and quantum chemistry simulations (ab initio molecular dynamics and density functional theory) allow us to characterise different fragmentation pathways as well as the associated mechanisms. We focus on the fragmentation of doubly ionised species, for which coincidence measurements provide unambiguous information on the origin of the various charged fragments. We have found that single N-methylation leads to a larger variety of fragmentation channels than in no methylation of glycine, while double N-methylation effectively closes many of these fragmentation channels, including some of those appearing in pristine glycine. Importantly, the closure of fragmentation channels in the latter case does not imply a protective effect by the methyl group.

We present a combined experimental and theoretical study of the fragmentation of singly and doubly

This work aims at exploring the potential energy surfaces of C

International audience; We propose to combine quantum chemical calculations, statistical mechanical methods, and photoionization and particle collision experiments to unravel the redistribution of internal energy of the furan cation and its dissociation pathways. This approach successfully reproduces the relative intensity of the different fragments as a function of the internal energy of the system in photoelectronphotoion coincidence experiments and the different mass spectra obtained when ions ranging from Ar + to Xe 25+ or electrons are used in collision experiments. It provides deep insights into the redistribution of the internal energy in the ionized molecule and its influence on the dissociation pathways and resulting charged fragments. The present pilot study demonstrates the efficiency of a statistical exchange of excitation energy among various degrees of freedom of the molecule and proves that the proposed approach is mature to be extended to more complex systems.

International audience; The breakup of a molecule following a fast collision with an atom in gas phase can be understood as resulting from two steps. In the first step, the atom transfers energy to the molecule, which is thus electronically and vibrationally excited. In the second step, the molecule decays leading to different fragments, while the initial charge, energy, and angular momentum are conserved. Here, we demonstrate that, by maximizing the entropy of the system under these conservation laws, it is possible to reproduce the fragmentation yields resulting from collision experiments. In particular, our model is applied to investigate fragmentation of excited neutral and singly charged carbon clusters and mono-hydrogenated carbon clusters. These species are commonly exposed to energetic ionizing radiation in the interstellar medium, so understanding the key aspects of their fragmentation, in particular the way energy and charge are shared in the process, can be relevant to get a deeper insight on the evolution of carbonaceous species in the universe.

The European physical journal / D 75(5), 152 (2021). doi:10.1140/epjd/s10053-021-00155-y, This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science., Published by Springer, Heidelberg

The way molecules break after ion bombardment is intimately related to the early electron dynamics generated in the system, in particular, charge (or electron) migration. We exploit the natural positive-negative charge splitting in the zwitterionic molecule betaine to selectively induce double electron removal from its negatively charged side by impact of fast O

This work aims at exploring the potential energy surfaces of C$_{24}$H$_n${n=0,6,12,18,24} up to 20-25\,eV using the genetic algorithm in combination with the density functional based tight binding (DFTB) potential. The structural diversity of the non fragmented structures was analysed using order parameters which were chosen as the number of 5 or 6 carbon rings and the asphericity constant $\beta$. The most abundant and lowest energy population was found to correspond to a flakes population, constituted of isomers of variable shapes possessing a large number of 5 or 6-carbon rings. This population is characterized by a larger number of spherical isomers when $n_H/n_C$ increases. Simultaneously, the fraction of the pretzels population constituted of spherical isomers possessing fewer 5 or 6 carbon ring cycles increases. For all hydrogenation rates, the fraction of cages population remains extremely minor while the branched population is the highest energy population for all $n_H/n_C$ ratios. For all C$_{24}$H$_n${n=0,6,12,18,24} clusters, a detailed study of the evolution of the carbon ring size distribution as a function of energy clearly shows that the stability is correlated to the number of 6-carbon rings. A similar study for hybridization $sp^n$ (n=1-3) shows that the number of $sp^1$ carbon atoms increases with energy while globally the number of $sp^3$ carbon atoms increases with $n_H/n_C$. The average values of the ionization potentials of all populations were found to decrease when $n_H/n_C$ increases, ranging from 7.9\,eV down to 6.4\,eV that we correlated to carbon atoms hybridization $sp^n$ (n=1-3). These results are of astrophysical interest as they should be taken into account in astrophysical models especially regarding the role of carbonaceous species in the gas ionization., Comment: 37 pages, 13 figures

We present a theoretical study on the thermodynamic and kinetic reactivity of Diels-Alder cycloadditions to several empty fullerenes in order to investigate the relationship between reaction energies and energy barriers. The results show that fullerenes with large HOMO-LUMO gaps present good correlation coefficients. In all other cases, two factors are responsible for the lack of correlation. First, the formation of unexpected adducts which are not the ones resulting from a [4+2] addition and second the change in the electronic structure of some adducts due to the mixing of the ground state with excited states close in energy.

The scientific community and regulatory bodies worldwide, currently promote the development of non-experimental tests that produce reliable data for pesticide risk assessment. The use of standard quantum chemistry methods could allow the development of tools to perform a first screening of compounds to be considered for the experimental studies, improving the risk assessment. This fact results in a better distribution of resources and in better planning, allowing a more exhaustive study of the pesticides and their metabolic products. The current paper explores the potential of quantum chemistry in modelling toxicity and environmental behaviour of pesticides and their by-products by using electronic descriptors obtained computationally. Quantum chemistry has potential to estimate the physico-chemical properties of pesticides, including certain chemical reaction mechanisms and their degradation pathways, allowing modelling of the environmental behaviour of both pesticides and their by-products. In this sense, theoretical methods can contribute to performing a more focused risk assessment of pesticides used in the market, and may lead to higher quality and safer agricultural products. © 2017 Society of Chemical Industry.

A simple model, based on connectivity (adjacency) matrices, is introduced to study the relative stability of hydrogenated polycyclic aromatic hydrocarbons (HPAHs). The model allows us to consider a very large number of isomeric structures for HPAHs of variable size and degree of hydrogenation, by taking into account the different positions available in each hydrogenation step. The validity of our approach is demonstrated by comparing, for a few selected cases, with the predictions of Density Functional Theory calculations. We have found that aromaticity is the main factor governing the relative stability of HPAH isomers and that the most stable structures are in general those containing the maximum possible number of non-hydrogenated rings.

Synopsis The main objective of this study is to determine the energy transfer occuring in ion-molecule collisions. In order to solve this problem, we followed two approaches; the first one by validating a purely experimental method and the second one by testing a new theoretical model M3C (Microcanonical Metropolis Monte Carlo).

Helium has a unique phase diagram and below 25 bar it does not form a solid even at the lowest temperatures. Electrostriction leads to the formation of a solid layer of helium around charged impurities at much lower pressures in liquid and superfluid helium. These so-called ‘Atkins snowballs' have been investigated for several simple ions. Here we form HenC60+ complexes with n exceeding 100 via electron ionization of helium nanodroplets doped with C60. Photofragmentation of these complexes is measured by merging a tunable narrow-bandwidth laser beam with the ions. A switch from red- to blueshift of the absorption frequency of HenC60+ on addition of He atoms at n=32 is associated with a phase transition in the attached helium layer from solid to partly liquid (melting of the Atkins snowball). Elaborate molecular dynamics simulations using a realistic force field and including quantum effects support this interpretation., 'Atkins snowballs', solid layers of helium around an ion core in bulk superfluid He, have been investigated for simple ions but many properties remain unknown. Here, the authors show via photofragmentation experiments that a phase transition occurs in C60-doped He droplets depending on the number of He atoms.

Direct decomposition of NO on an open flat Ru(1011) surface is investigated using density functional theory. The calculations show that for this surface, dissociation barriers are very low, adsorption energies of the corresponding atomic products are almost site-independent, and atomic diffusion barriers are quite low. As a consequence, the Ru(1011) surface is more reactive than the flat Ru(0001) surface and has more active sites than surface steps. This conclusion opposes the general view that step edges or defects are the optimum sites for molecular dissociation and, therefore, points to new directions to improve the performance of existing catalysts.

International audience; The Microcanonical Metropolis Monte Carlo (MMMC) method has been shown to describe reasonably well fragmentation of clusters composed of identical atomic species. However, this is not so clear in the case of heteronuclear clusters as some regions of phase space might be inaccessible due to the different mobility of the different atomic species, the existence of large isomerization barriers, or the quite different chemical nature of the possible intermediate species. In this paper, we introduce a constrained statistical model that extends the range of applicability of the MMMC method to such mixed clusters. The method is applied to describe fragmentation of isolated clusters with high, moderate, and no heteronuclear character, namely, CnHm, CnN, and Cn clusters for which experimental fragmentation branching ratios are available in the literature. We show that the constrained statistical model describes fairly well fragmentation of CnHm clusters in contrast with the poor description provided by the fully statistical model. The latter model, however, works pretty well for both Cn and CnN clusters, thus showing that the ultimate reason for this discrepancy is the inability of the MMMC method to selectively explore the whole phase space. This conclusion has driven us to predict the fragmentation patterns of the C4N cluster for which experiments are not yet available

Endohedral metallofullerenes (EMFs) synthetized in the laboratory are known to often violate the isolated pentagon and pentagon adjacency penalty rules that successfully describe the relative stability of pristine fullerene isomers. To explain these anomalies, several models have been proposed. In this work, we have systematically investigated the performance of the widely used IPSI (inverse pentagon separation index), ALA (additive local aromaticity) and CSI (charge stabilization index) models in predicting the relative stability of a large number of EMF isomers with cages ranging from C28 to C104 and charge states of 4- and 6-. By explicitly comparing with existing experiments and quantum chemistry calculations, we show that the predictive power of the ALA and CSI models is similarly good, with CSI being slightly superior though computationally much less involved. IPSI's performance is generally worse though still acceptable in a wide range of cage sizes, except for the higher charge states in the C62 to C82 size interval. From our analysis, we conclude that neither Coulomb electronic repulsion (IPSI) nor aromaticity (ALA) are the sole parameters governing the relative stability of EMF isomers. Electron delocalization in the π shell in combination with minimum strain (CSI) provides a more realistic description of the relative stabilities observed experimentally, as the former can compensate an unfavorable Coulomb repulsion and account for stabilizing binding effects that do not necessarily translate into aromaticity.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Chemical Physics 151.4 (2019): 044306 and may be found at https://aip.scitation.org/doi/abs/10.1063/1.5109963, We have measured fragment mass spectra and total destruction cross sections for protonated and deprotonated adenine following collisions with He at center-of-mass energies in the 20-240 eV range. Classical and ab initio molecular dynamics simulations are used to provide detailed information on the fragmentation pathways and suggest a range of alternative routes compared to those reported in earlier studies. These new pathways involve, for instance, losses of HNC molecules from protonated adenine and losses of NH2 or C3H2N2 from deprotonated adenine. The present results may be important to advance the understanding of how biomolecules may be formed and processed in various astrophysical environments, This work was supported by the Swedish Research Council (Constant Nos. 2017-00621, 2015-04990, 2016-04181, and 2018-04092). Furthermore, we acknowledge the European Joint on Theoretical Chemistry and Computational Modelling (INT-EJD-TCCM). We acknowledge the generous allocation of computer time at the Centro de Computacion Cientifica at the Universidad Autonoma de Madrid (CCC-UAM). This work was partially supported by Project No. CTQ2016-76061-P of the Spanish Ministerio de Economia y Competitividad (MINECO)

We present a complete exploration of the different fragmentation mechanisms of furan (C4H4O) operating at low and high energies. Three different theoretical approaches are combined to determine the structure of all possible reaction intermediates, many of them not described in previous studies, and a large number of pathways involving three types of fundamental elementary mechanisms: isomerization, fragmentation, and H/H2 loss processes (this last one was not yet explored). Our results are compared with the existing experimental and theoretical investigations for furan fragmentation. At low energies the first processes to appear are isomerization, which always implies the breaking of one C–O bond and one or several hydrogen transfers; at intermediate energies the fragmentation of the molecular skeleton becomes the most relevant mechanism; and H/H2 loss is the dominant processes at high energy. However, the three mechanisms are active in very wide energy ranges and, therefore, at most energies there is a c...

In this work we present a density functional theory study of the interaction between a positively charged exohedral metallofullerene and several hydrogen molecules. For this purpose we have chosen Li+, Ti+, V+ and Cu+ as the metal cations, since they represent a good sample of ionic or covalent interactions with the carbon cage. We have found that the interaction between the hydrogen molecules and the metal cation strongly depends on the type of interaction between the metal cation and the fullerene. Furthermore, the hydrogen saturation around the metal is also determined by the nature of the metal.

We present a theoretical study of the adsorption of benzene C6H6 on the Cu(100) metal surface. The insulating effect of ionic films on this system has also been investigated by adsorbing C6H6 on the same surface covered with 1, 2, and 3 monolayers of NaCl. For this purpose, we employed density functional theory (DFT) including the van der Waals dispersion forces via a DFT-D2 scheme. For all the studied systems we analyzed the adsorption energies and geometries as well as the density of states in order to get a complete description of the type of binding, the charge transfer between the molecule and the surface, and the electronic level alignment after adsorption. We show that the molecule-substrate interaction is weak and mainly governed by dispersion forces, with an almost insignificant charge transfer between the substrate and the adsorbate. We found a progressive decoupling of the molecule from the metal surface when the size of the ultrathin insulating NaCl film increases.

Understanding the relationship between structure and stability is one of the fundamental aspects of fullerene chemistry, as the number of possible cage isomers is very large and complexity increases by orders of magnitude when chemical groups are attached to the fullerene cage. The well-established stability rules valid for neutral fullerenes do not apply to many charged or functionalized fullerenes. Here we present the theory, implementation, and applications of two simple topology-based models that allow one to predict the relative stability of charged and functionalized fullerenes without the need for quantum chemistry calculations: (i) the charge stabilization index (CSI) model, based on the concepts of cage connectivity and frontier π orbitals, which offers a general framework for the relative stability of both positively and negatively charged fullerenes, as well as endohedral metallofullerenes, and (ii) the exohedral fullerene stabilization index (XSI) model, which incorporates all key factors governing the stability of exohedral fullerenes, namely, π delocalization, σ strain, and steric hindrance between addends. Based exclusively on topological information, both models are powerful prescreening tools for predicting the most stable structures of a large number of charged and functionalized fullerenes. For easy use by fullerene chemists, both models have been implemented in the FullFun (for Fullerene Functionalization) software package, whose effectiveness and efficiency are demonstrated by some illustrative examples.

We present an extensive and systematic study on the regioselectivity of Diels-Alder (DA) cycloadditions to empty fullerenes, covering the whole range of cage sizes from C60 to C180. Reaction energies obtained from DFT calculations, which correlate with activation barriers, can be well reproduced by using a simple Hückel model, indicating that π electronic effect is the key factor determining the relative stability of DA adducts. Based on these results, we propose a couple of simple rules of thumb, in terms of a set of bond patterns, as a visual guide for approximate prediction of DA reactive sites. Moreover, we suggest two quantitative descriptors for the stability of DA regioadducts of empty fullerenes; one combines the π free valences and bond orders involved in the DA addition, and the other characterizes the local π aromaticity around the addition site. The latter criterion allows us to easily rationalize the proposed rules.

Density functional theory calculations allowed us to study alloxydim herbicide and to identify the most stable conformers, the factors that governs their stability, and the interconversion mechanisms among the most relevant conformers. The degradation chain involves, as a first step, the cleavage of the N-O bond and the formation of a stable intermediate difficult to characterize experimentally. The study performed also allowed us to identify the properties of this elusive intermediate and to determine that the dominant fragmentation process in the gas phase is the homolytic fragmentation. Stability of alloxydim conformers and homolytic fragments were also assessed in the water phase. Computed IR spectra were consistent with those observed experimentally.

Density Functional Theory was used to explore the protonation of the amine/imine byproducts of the alloxydim herbicide. An extensive exploration of the possible protonation sites of anionic and neutral fragments was performed. Doubly charged species were also considered. The structure and relative stabilities of different tautomers were determined. Computed infrared spectra allowed a better understanding of the vibrational modes and were consistent with those observed experimentally. Calculated UV–Vis spectra allow to predict a probable further photodegradation.

We present a combined experimental and theoretical study of the fragmentation of doubly positively charged b-alanine molecules in the gas phase. The dissociation of the produced dicationic molecules, induced by low-energy ion collisions, is analysed by coincidence mass spectrometric techniques; the coupling with ab initio molecular dynamics simulations allows rationalisation of the experimental observations. The present strategy gives deeper insights into the chemical mechanisms of multiply charged amino acids in the gas phase. In the case of the b-alanine dication, in addition to the expected Coulomb explosion and hydrogen migration processes, we have found evidence of hydroxyl-group migration, which leads to unusual fragmentation products, such as hydroxymethyl cation, and is necessary to explain some of the observed dominant channels, Financial support received from the CNRS PICS-05356 program, the ANR Programme Blanc PIBALE/ANR-09-BLAN-013001. Work was partially supported by the projects FIS2013-42002-R and CTQ2013-43698-P (MINECO), and NANOFRONTMAG (CAM). D.G.P. acknowledges the support of the Erasmus Mundus program of the European Union (FPA 2010-0147)

Organic charge transfer (CT) compounds display a wide range of exotic electronic properties (charge-density wave stabilization, Peierls transitions, etc.) depending on the amount of charge transferred from the donor (D) to the acceptor (A) species. A complete exploration of the complex electronic phase diagrams for such compounds would thus require methods to systematically tune the amount of charge exchanged in the CT process. This has proven however challenging in the past: chemical functionalization of the constituent molecules can also affect the packing of the molecular units in the crystal, whereas changing D:A stoichiometry is often not possible in the bulk. Interestingly, it was recently found that multiple stoichiometries can actually be achieved by codeposition of different amounts of D and A molecules on metal surfaces. The question, however, of whether CT processes between D and A molecules can be tuned with the D:A ratio in such mixtures has not yet been studied, and it is no trivial matter, since competing CT processes between the metal surface and the organic adsorbates might hinder interadsorbate charge transfer. Here we demonstrate that the CT process from the organic donor tetrathiafulvalene (TTF) to the acceptor tetracyanoquino-p-dimethane (TCNQ) can be tuned with exquisite accuracy (∼0.1 e) by controlling the stoichiometry of D:A cocrystals deposited on Ag(111). This control opens new avenues to explore the complex phase diagrams of organic CT compounds and to tailor their electronic properties., The authors acknowledge financial support from the Spanish Ministry for Economy and Competitiveness (Grants FIS2012-33011, FIS2015-67367-C2-1-P, FIS2013-42002-R, FIS2016-77889-R, CTQ2013-43698-P, CTQ2016-76061-P), the regional government of Comunidad de Madrid (Grants S2009/MAT1726 and S2013/MIT-3007), Universidad Autónoma de Madrid (UAM/48) and IMDEA Nanoscience. L.F. acknowledges financial support from MIUR (PRIN-2010BNZ3F2, Project DESCARTES), S.D.-T. acknowledges the ‘“Ramón y Cajal”’ program of the MINECO (RYC-2010-07019), and the María de Maeztu Programme for Units of Excellence in R&D of the MINECO (MDM-2014-0377).

We present an extension of the structural motif model [Cioslowski et al., J. Am. Chem. Soc., 2000, 122, 8265], originally proposed to predict the relative stability of medium-sized neutral fullerenes (C

We present a combined experimental and theoretical study of the fragmentation of multiply-charged γ-aminobutyric acid molecules (GABA

The scientific community and regulatory bodies worldwide, currently promote the development of non-experimental tests that produce reliable data for pesticide risk assessment. The use of standard quantum chemistry methods could allow the development of tools to perform a first screening of compounds to be considered for the experimental studies, improving the risk assessment. This fact results in a better distribution of resources and in better planning, allowing a more exhaustive study of the pesticides and their metabolic products. The current paper explores the potential of quantum chemistry in modelling toxicity and environmental behaviour of pesticides and their by-products by using electronic descriptors obtained computationally. Quantum chemistry has potential to estimate the physico-chemical properties of pesticides, including certain chemical reaction mechanisms and their degradation pathways, allowing modelling of the environmental behaviour of both pesticides and their by-products. In this sense, theoretical methods can contribute to performing a more focused risk assessment of pesticides used in the market, and may lead to higher quality and safer agricultural products. © 2017 Society of Chemical Industry.

Synopsis This work relies on complementary theoretical and experimental studies of the processes induced by ion-furan collisions. Results of the Molecular Dynamics simulations and exploration of the energy profiles combined with coincidence mass spectrometry provide complete picture of the fragmentation of furan dication.

Predicting and understanding the relative stability of exohedral fullerenes is an important aspect of fullerene chemistry, since the experimentally formed structures do not generally follow the rules that govern addition reactions or the making of pristine fullerenes. First-principles theoretical calculations are of limited applicability due to the large number of possible isomeric forms, for example, more than 50 billion for C60X8. Here we propose a simple model, exclusively based on topological arguments, that allows one to predict the relative stability of exohedral fullerenes without the need for electronic structure calculations or geometry optimizations. The model incorporates the effects of π delocalization, cage strain, and steric hindrance. We show that the subtle interplay between these three factors is responsible for (i) the formation of non-IPR (isolated pentagon rule) exohedral fullerenes in contrast with their pristine fullerene counterparts, (ii) the appearance of more pentagon–pentagon ad...

The deposition of large amounts of energy in a molecule by XUV/X-ray photon absorption or fast-ion collision, triggers a set of complex ultrafast electronic and nuclear dynamics that allow a deep understanding and control of chemical reactivity. This themed issue showcases the research performed in the understanding, monitoring and control of these processes.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Chemical Theory and Computation, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to Published Work, see http://pubs.acs.org/doi/abs/10.1021/acs.jctc.6b00984, The Microcanonical Metropolis Monte Carlo method, based on a random sampling of the density of states, is revisited for the study of molecular fragmentation in the gas phase (isolated molecules, atomic and molecular clusters, complex biomolecules, etc.). A random walk or uniform random sampling in the configurational space (atomic positions) and a uniform random sampling of the relative orientation, vibrational energy, and chemical composition of the fragments is used to estimate the density of states of the system, which is continuously updated as the random sampling populates individual states. The validity and usefulness of the method is demonstrated by applying it to evaluate the caloric curve of a weakly bound rare gas cluster (Ar13 ), to interpret the fragmentation of highly excited small neutral and singly positively charged carbon clusters (Cn , n = 5,7,9 and Cn+, n = 4,5) and to simulate the mass spectrum of the acetylene molecule (C2H2 ), Work was supported by the MINECO projects FIS2013-42002-R and CTQ2013-43698-P the CAM project NANOFRONTMAG-CM ref S2013/MIT-2850S, and the European COST Action CM1204 XLIC. S.D.-T. gratefully acknowledges the Ramon y Cajal program of the Spanish MINECO. Financial support from the Spanish Ministry of Economy and Competitiveness, through The Maria de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377) is acknowledged

We present an extension of the structural motif model [Cioslowski et al., J. Am. Chem. Soc., 2000, 122, 8265], originally proposed to predict the relative stability of medium-sized neutral fullerenes (C60–C102), to account for the correct graphene limit, thus widening its range of applicability to giant and supergiant icosahedral fullerenes. The new model has been parameterized using the density functional theory (DFT) energies of 426 distinct fullerenes ranging from C60 to C180, most of which correspond to the lowest-energy isomers of each cage size. While the original model is inapplicable for fullerenes larger than C150, the new model performs very well for these systems, with typical deviations of 3.4 kcal mol−1 from the DFT energies. Based on the optimized parameters, we have obtained the actual energy contributions for all motifs, which we show are closely related to the number and separation of pentagonal rings, in contrast to the original version of the model. We also point out that, in general, motif models result in large deviations for largely aspherical fullerenes and propose a way to correct the errors.

The Microcanonical Metropolis Monte Carlo method, based on a random sampling of the density of states, is revisited for the study of molecular fragmentation in the gas phase (isolated molecules, atomic and molecular clusters, complex biomolecules, etc.). A random walk or uniform random sampling in the configurational space (atomic positions) and a uniform random sampling of the relative orientation, vibrational energy, and chemical composition of the fragments is used to estimate the density of states of the system, which is continuously updated as the random sampling populates individual states. The validity and usefulness of the method is demonstrated by applying it to evaluate the caloric curve of a weakly bound rare gas cluster (Ar

This is the peer reviewed version of the following article: Advanced Materials 28.30 (2016): 6332-6336, which has been published in final form at http://dx.doi.org/10.1002/adma.201602128. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving, Antimonene fabricated by mechanical exfoliation is highly stable under atmospheric conditions over periods of months and even when immersed in water. Density functional theory confirms the experiments and predicts an electronic gap of ≈1 eV. These results highlight the use of antimonene for optoelectronics applications, This work was supported by MINECO projects Consolider CSD2010-00024, MAT2013- 46753-C2-1 and 2, FIS2013-42002-R and CTQ2013-43698-P, CAM project NANOFRONTMAG-CM (ref. S2013/MIT-2850)

The ionization and fragmentation of the nucleoside thymidine in the gas phase has been investigated by combining ion collision with state-selected photoionization experiments and quantum chemistry calculations. The comparison between the mass spectra measured in both types of experiments allows us to accurately determine the distribution of the energy deposited in the ionized molecule as a result of the collision. The relation of two experimental techniques and theory shows a strong correlation between the excited states of the ionized molecule with the computed dissociation pathways, as well as with charge localization or delocalization, We thank F. Noury, S. Guillous, R. Richter, M. Coreno, and K. Prince for support as well as L. J. Avaldi for advice in the statistical analysis of the data. We acknowledge the allocation of computer time at the Centro de Computación Científica at the Universidad Autónoma de Madrid (CCCUAM). This work was partially supported by the projects FIS2013-42002-R and CTQ2013-43698-P (MINECO), NANOFRONTMAG (CAM), PHC Galilée 28137PE, and an Advanced Grant of the European Research Council XCHEM No. 290853. Research was conducted in the framework of the International Associated Laboratory (LIA) “Fragmentation dynamics of complex molecular systems—DYNAMO” and in the COST actions XLIC (CM1204) and Nano-IBCT (MP1002). D. G. P. acknowledges the FPI grant of the Universidad Autónoma de Madrid. S. D.-T. gratefully acknowledges the “Ramón y Cajal” program of the Spanish Ministerio de Educación y Ciencia

On page 6332, J. Gomez-Herrero, F. Zamora, and co-workers describe the isolation of antimonene, a new allotrope of antimony that consists of a single layer of atoms. They obtain antimonene flakes by the scotch tape method; these flakes are highly stable in ambient conditions and even when immersed in water. The 1.2 eV gap calculated in this study suggests potential applications in optoelectronics.

The fullerene-50 is a 'magic number' cage according to the 2(N + 1)(2) rule. For the three lowest isomers of C50 with trigonal and pentagonal symmetries, we calculate the sphericity index, the spherical parentage of the occupied π-orbitals, and the current density in an applied magnetic field. The minimal energy isomer, with D3 symmetry, comes closest to a spherical aromat or a superaromat. In the D5h bond-stretch isomers the electronic structure shows larger deviations from the ideal spherical shells, with hybridisation or even reversal of spherical parentages. It is shown that relative stabilities of fullerene cages do not correlate well with aromaticity, unlike the magnetic properties which are very sensitive indicators of spherical aromaticity. Superaromatic diamagnetism in the D3 cage is characterized by global diatropic currents, which encircle the whole cage. The breakdown of sphericity in the D5h cages gives rise to local paratropic countercurrents. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Ana Sanz Matías (ResearcherID) copyright_licence: The PCCP Owner Societies have an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported Licence (CC BY-NC 3.0) history: Received 20 August 2015; Accepted 23 September 2015; Accepted Manuscript published 28 September 2015; Advance Article published 7 October 2015; Version of Record published 28 April 2016 ispartof: Physical Chemistry Chemical Physics vol:18 issue:17 pages:11653-11660 ispartof: location:England status: published

We present a systematic density functional theory (DFT) study of the isolated manganese-phthalocyanine, MnPc, by using both localized gaussian-type orbital (GTO) and plane-wave (PW) basis sets and the following exchange-correlation functionals: B3LYP, PBE, PBE0, HSE, and HSE06. We find a very good agreement between GTO and PW results, which is a necessary condition in order to extend the present methodology to MnPc molecules deposited on metal surfaces. We conclude that the HSE06 functional is the most suitable one for the study of MnPc/inorganic interfaces with a basis of plane waves. We compare our calculated electron energy spectra with two available experiments [Kraus et al. in Chem Phys Lett 469:121, 2009; Grobosch et al. in Organics Electron 11:1483, 2010; Papageorgiou et al. in Prog Surf Sci 77:139, 2004] in which the ultraviolet photoemission spectra (UPS) have been measured. Our results suggest that spectra obtained from MnPc molecules in the gas phase are closer to those obtained from thin films of MnPc deposited on inert surfaces than to those obtained from thick films. Finally, we report optical absorption spectra by using a time-dependent DFT approach. Our results are again compatible with measurements performed on thin MnPc films.

We report a DFT study on the self-assembly of the fullerene derivative PCBM on the Au(111) surface. Recent STM experiments (Angew. Chem. 2007, 119, 8020-8023 [1] ) show a coverage-dependent transition of the adsorption and self-assembly of PCBM on this surfaces. To understand the origin of this observation, we compute the geometries and relative energies of ten PCBM dimers and four tetramers. The calculations show that the self-assembly of PCBM at high coverage is mainly controlled by hydrogen bonding between the PCBM tails. Due to the large size of the fullerene cage, the hydrogen bonds are formed far away from the surface; hence they are very similar to those found in the gas phase. This picture successfully explains the observed site-insensitive adsorption at high coverage and the 2D arrangement of PCBM on the surface.

We show that the relative isomer stability of fullerene anions is essentially governed by a few simple structural motifs, requiring only the connectivity information between atoms. Relative energies of a large number of isomers of fullerene anions, C(2n)(q) (2n = 68-104; q = -2, -4, -6), can be satisfactorily reproduced by merely counting the numbers of seven kinds of hexagon-based motifs. The dependence of stability on these motifs varies with the charge state, which reflects the fact that the isomeric form of the carbon cage in endohedral metallofullerenes (EMFs) often differs from that in neutral empty fullerenes. The chemical origin of the stabilization differences between motifs is discussed on the basis of electronic and strain effects as well as aromaticity. On the basis of this simple model, the extraordinary abundance of the icosahedral C80 cage in EMFs can be easily understood. We also provide an explanation for why the well-known isolated pentagon rule is often violated in smaller EMFs. Finally, simple topological indices are proposed for quantitatively predicting the relative stability of fullerene anions, allowing a rapid determination of suitable hosting cages in EMFs by just counting three simple structural motifs.

The fragmentation of doubly charged gas-phase methionine (HO2CCH(NH2)CH2CH2SCH3) is systematically studied using the self-consistent charge density functional tight-binding molecular dynamics (MD) simulation method. We applied graph theory to analyze the large number of the calculated MD trajectories, which appears to be a highly effective and convenient means of extracting versatile information from the large data. The present theoretical results strongly concur with the earlier studied experimental ones. Essentially, the dication dissociates into acidic group CO2H and basic group C4NSH10. The former may carry a single or no charge and stays intact in most cases, whereas the latter may hold either a single or a double charge and tends to dissociate into smaller fragments. The decay of the basic group is observed to follow the Arrhenius law. The dissociation pathways to CO2H and C4NSH10 and subsequent fragmentations are also supported by ab initio calculations.