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A detailed quantum chemical investigation of a new reaction mechanism possibly leading to the formation of cyanoketene (NC–CH═C═O) in the interstellar medium (ISM) was carried out. Different reaction channels have been found by the AutoMeKin program, and the structures and harmonic force fields of the key stationary points have been characterized at the density functional theory level employing last-generation double-hybrid functionals. Finally, single-point computations at those geometries by state-of-the-art composite wave function methods provided accurate energies for the evaluation of thermochemical and kinetic parameters in the framework of an Ab Initio Transition State Theory based Master Equation (AITSTME) strategy. Our results indicate that the barrier-less association reaction of the formyl radical (HCO•) to the cyanocarbene radical (HCCN) can lead to the formation of cyanoketene under the harsh conditions of the ISM. Canonical rate constants computed for temperatures up to 600 K show that the most abundant product is indeed cyanoketene. The formation of other, even more stable, species involves higher activation energies and/or less favorable multi-step processes. Furthermore, to aid the search of cyanoketene, still undetected in the ISM, its rotational spectrum was recorded up to 530 GHz. The refined set of spectroscopic constants obtained in this way allows for spectral predictions from the microwave to the terahertz region, particularly for the bright b-type transitions, which can be targeted for the identification of cyanoketene in spectral line surveys. Despite cyanoketene was already sought without success in a variety of astronomical sources, we suggest to look for it in those sources where HCO or HCCN have already been detected, namely, W3, NGC2024, W51, K3-50, IRC + 2016, and TMC-1.

The scaled roto-diffusion tensor that includes dissipative and energetic properties of a molecule introduced here describes molecular local and global flexibility allowing a rigorous hierarchical selection of the relevant dynamics.

Cyanoacetaldehyde (NC-CH2CH=O) is considered, together with guanidine and urea, as a precursor of the pyrimidine bases cytosine and uracil. Although it has not yet been detected in the interstellar medium (ISM), several hypotheses have been put forward about its synthesis in solution and in the gas phase. In this paper, we present a gas-phase model of the barrierless reaction between formyl (HCO) and cyanomethyl (CH2CN) radicals leading to cyanoacetaldehyde and focus on its evolution through isomerization and dissociation pathways. The potential-energy surface for all reactions has been explored by DFT calculations employing double-hybrid functionals and further refined through the "Cheap" composite scheme. Our results indicate that the direct association of the two reacting radicals (HCO and CH2CN) is strongly exothermic and thus thermodynamically favored under the harsh conditions of the ISM. Microcanonical rate constants computed with the help of the StarRate program for energies up to 6 kJ mol(-)(1) above the dissociation limit show that the most abundant products are the two conformers of cyanoacetaldehyde (nitrile and carbonyl groups in a cis or trans configuration) which, despite having comparable stability, are obtained with a cis/trans ratio of 0.35:0.65. The formation of other products with relative abundances not exceeding 10% is also discussed.

THE ''LIfe in Space'' project was funded in the wake of the Italian Space Agency's proposal for the development of a network of institutions and laboratories conceived to implement Italian participation in space astrobiology experiments. Of primary concern for this project is the study of the origin of life in the Universe, a focus that will promote investigation into prebiotic chemistry in various possible scenarios, whether in polar or nonpolar solvents (e.g., Titan's environment). Such results will link with study of the effects of simulated space conditions on possible chemical bio- signatures. The limits of life as we know it will be investigated in ground-based experiments with microorganisms that have already demonstrated their resistance to extreme environments on Earth and to real or simulated space conditions. The potential survival of microorganisms will also be examined with up-to-date molecular methods. The ability of some microorganisms to produce atmospheric and surface biosignatures when exposed to simulated conditions will be tested and compared with the possible existence of bio- signatures on potentially habitable exoplanets. Furthermore, the search for potentially habitable exoplanets, with space- based observational methods, will be optimized by way of dedicated climate models with the capacity to predict the detectability of atmospheric biosignatures for a broad range of planetary conditions. The project embraces the four most important topics in astrobiological research, as listed below, along with relevant contributions from the participating Italian institutions. Origins and evolution of organic compounds of biological significance in space (comets, asteroids, rocky planets, and moons); Prebiotic syntheses, origin of life, and early life; The limits of life and biological habitability: origin, evolution and adaptation of life in extreme environments on Earth and in space; Biomarkers for life detection in the Solar System and on exoplanets.

A framework for the stochastic description of relaxation processes in flexible macromolecules including dissipative effects has been recently introduced, starting from an atomistic view, describing the joint relaxation of internal coordinates and global degrees of freedom, and depending on parameters recoverable from classic force fields (energetics) and medium modelling at the continuum level (friction tensors). The new approach provides a rational context for the interpretation of magnetic resonance relaxation experiments. In its simplest formulation, the semi-flexible Brownian (SFB) model has been until now shown to reproduce correctly correlation functions and spectral densities related to orientational properties obtained by direct molecular dynamics simulations of peptides. Here, for the first time, we applied directly the SFB approach to the practical evaluation of high-quality 13C nuclear magnetic resonance relaxation parameters, T1 and T2, and the heteronuclear NOE of several oligosaccharides, which were previously interpreted on the basis of refined ad hoc modelling. The calculated NMR relaxation parameters were in agreement with the experimental data, showing that this general approach can be applied to diverse classes of molecular systems, with the minimal usage of adjustable parameters.

A gas-phase nitrogen-nitrogen noncovalent interaction has been unveiled in the nitroethane-trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C-H⋅⋅⋅O and C-H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination.

Through an analysis of eighty tetrahedral and square-planar metal carbonyls of general formula [M(CO)(L0)(L)2] including newly synthesized chlorocarbonyl rhodium complexes with chelating atropoisomeric diphosphanes, we show how coordination geometry can switch the carbonyl stretching frequency into a selective probe of the r-donor and p-acceptor abilities of the ligands. We thus provide a framework whereby the r-donation and p-backdonation constituents of the Dewar–Chatt–Duncanson model can be quantitatively predicted through spectroscopic data on coordinated CO moieties and vice versa.

The virtual-reality framework AVATAR (Advanced Virtual Approach to Topological Analysis of Reactivity) for the immersive exploration of potential-energy landscapes is presented. AVATAR is based on modern consumer-grade virtual-reality technology and builds on two key concepts: (a) the reduction of the dimensionality of the potential-energy surface to two process-tailored, physically meaningful generalized coordinates, and (b) the analogy between the evolution of a chemical process and a pathway through valleys (potential wells) and mountain passes (saddle points) of the associated potential energy landscape. Examples including the discovery of competitive reaction paths in simple A + BC collisional systems and the interconversion between conformers in ring-puckering motions of flexible rings highlight the innovation potential that augmented and virtual reality convey for teaching, training, and supporting research in chemistry.

Chemical bonding in a set of six cuprous complexes with simple nitriles (CN−, HNC, HCN, CH3NC, and CH3CN) is investigated by means of a recently devised analysis scheme framed in density-functional theory and quantitatively singling out concurrent charge flows such as σ donation and π backdonation. The results of our analysis are comparatively assessed against qualitative models for charge redistribution based on the popular concepts of octet rule and resonance structures, and the relative importance of different charge-flow channels relating to σ donation, π back-donation, polarization, and hyperconjugation is discussed on a quantitative basis.

We present a four-component relativistic density functional theory study of the chemical bond and s–d hybridization in the group 11 cyanides M–CN (M = Cu, Ag, and Au). The analysis is carried out within the charge-displacement/natural orbital for chemical valence (CD-NOCV) scheme, which allows us to single out meaningful contributions to the total charge rearrangement that arises upon bond formation and to quantify the components of the Dewar–Chatt–Duncanson bonding model (the ligand-to-metal donation and metal-to-ligand back-donation). The M–CN bond is characterized by a large donation from the cyanide ion to the metal cation and by two small back-donation components from the metal toward the cyanide anion. The case of gold cyanide elucidates the peculiar role of the relativistic effects in determining the characteristics of the Au–C bond with respect to the copper and silver homologues. In AuCN, the donation and back-donation components are significantly enhanced, and the spin–orbit coupling, removing the degeneracy of the 5d atomic orbitals, induces a substantial split in the back-donation components. A simple spatial analysis of the NOCV-pair density, related to the ligand-to-metal donation component, allows us to quantify, with unprecedented accuracy, the charge rearrangement due to the s–d hybridization occurring at the metal site. The s–d hybridization plays a key role in determining the shape and size of the metal; it removes electron density from the bond axis and induces a significant flattening at the metal site in the position trans to the ligand. The s–d hybridization is present in all noble metal complexes, influencing the bond distances, and its effect is enhanced for Au, which is consistent with the preference of gold to form linear complexes. A comparative investigation of simple complexes [AuL]+/0of Au+with different ligands (L = F–,N-heterocyclic carbene, CO, and PH3) shows that the s–d hybridization mechanism is also influenced by the nature of the ligand.

Ring-puckering motion in 12 flexible cyclic molecules is investigated by calculation and analysis of two-dimensional potential-energy surfaces (PESs) using the so-called ring-puckering coordinates proposed by Cremer and Pople. The PESs are calculated by means of density-functional theory using a B2PLYP-D3BJ exchange-correlation functional with a maug-cc-pVTZ basis set, and results are compared to the available experimental and theoretical data. Special care is devoted to the aspect of symmetry in such two-dimensional PESs, which are here reported for the first time also for molecules whose planar form has symmetry lower than D5h or C2v. The issue of PES fitting and that of solving the nuclear dynamics using ring-puckering coordinates are also addressed. Analytical formulations of the computed PESs using suitable functional forms with a limited set of parameters are provided.

The relation between spectroscopic observables and the detailed metal-ligand bonding features in chelation complexes is addressed using both experimental and state-of-the-art theoretical and computational methods. We synthesized and characterized a set of six nickel dicarbonyl complexes of general formula [Ni(CO)2(PP)], where PP is an atropoisomeric chelating diphosphine ligand. The analysis of the obtained experimental data and the basicity and oxidative potentials of the free ligands suggests a close relation between the donor ability of the chelating ligand and the carbonyl stretching frequencies observed in the complexes. We then use theory to unravel the detailed mechanisms of chelation-bond formation in terms of partial charge flows between the molecular orbitals of the fragments. By extending the promising, recently published natural orbitals for chemical valence/charge displacement (NOCV/CD) analysis scheme we provide a thorough, quantitative description of the several charge fluxes following the metal-ligand bond formation and demonstrate that the carbonyl stretching frequencies in the considered complexes selectively respond to the σ-donation charge flow from the phosphorus lone pairs of the ligands, with the frequency shift being in quantitative correlation with the extent of the ligand-to-metal charge transfer.

Circular dichroism spectra in the IR range (VCD = vibrational circular dichroism) and in the UV range (ECD = electronic circular dichroism) have been recorded for both enantiomers of simple mono-substituted ferrocenes containing chiral pendants: 1-acetoxyethylferrocene, 1, 1-methoxyethylferrocene, 2, and 1-hydroxyethylferrocene, 3; the related disubstituted 1,1′-bis(1-hydroxyethyl)ferrocene, 4, was also considered. These two types of spectra, with the support of DFT calculations, concur to unequivocally confirm the absolute configuration for 1-4. In particular, our computational results point out the clear advantage of using an anharmonic oscillator model for the interpretation of VCD spectra of chiral ferrocenes. Interesting conformational properties are either confirmed or established by the technique, like the eclipsed conformation of the two cyclopentadienyl rings and an intra-molecular interaction involving the OH for 3. For 4, NMR, VCD and IR spectra are compatible with dimer formation and in this case a distorted conformation is predicted. Of utmost importance for the absolute configuration assignment in mono-substituted ferrocenes, we were able to identify a diagnostic VCD band at 950 cm -1 and a (low intensity) ECD band that clearly indicate the absolute configuration of the whole series.

We discuss the design and implementation of StarRate, a modern-Fortran program for the calculation of chemical kinetics coupled to anharmonic vibrational perturbative treatments. The program is written in the F language, a carefully crafted subset of Fortran 95, and is conceived in an object-based programming paradigm, i.e. the set of object-oriented programming features supported by Fortran 90/95. StarRate is made up of three main modules handling the involved molecular species, the elementary reaction steps, and the whole reaction scheme. Input data are accessed through an XML interface based on a cross-code hierarchical data format granting interoperability with popular electronic-structure packages and with the graphical interface of the Virtual Multifrequency Spectrometer developed in our group. Data parsing is performed through versatile Python scripts. Test calculations on the isomerization reaction of C-cyanomethanimine using anharmonic densities of states obtained with a development version of Gaussian are reported together with an account of ongoing developments.

Predicting the values of the potential energy surface (PES) for a given chemical system is essential to running the associated dynamics and modeling its evolution in time. To the purpose of modeling chemical reactions involving few atoms, this task is usually accomplished by fitting or interpolating a set of energies computed at different nuclear geometries through accurate, though computationally demanding, quantum-chemical calculations. Among the several approaches for choosing an appropriate set of geometries and energies, a new scheme has been recently proposed (Rampino S, J Phys Chem A 120:4683–4692, 2016) which is based on a regular sampling in a space-reduced bond-order (SRBO) domain rather than in the more conventional bond-length (BL) domain. In this work we address the performances of four machine-learning (ML) models, as opposed to pure mathematical fitting or interpolation schemes, in predicting the PES of a three-atom system modeling an atom-diatom exchange reaction when coupled to the SRBO sampling scheme. The models (two ensemble-learning, an automated ML, and a deep-learning one), trained on both SRBO and BL datasets, are shown to perform better than popular fitting or interpolation schemes and to give the best results if coupled to SRBO data.

Chemistry is a visual discipline deeply relying on graphical representations for bringing the structure and behaviour of the microscopic world at the reach of our senses. Recent advances in computer graphics and the advent of immersive-virtual-reality technologies are creating great new opportunities in the way of conceiving these graphical representations and interacting with them. To seize these opportunities we have developed a virtual laboratory casting researchers amid the electron clouds of molecular systems and allowing them to perform a quantitative analysis of chemical bonding in an interactive and cooperative way. We discuss the developed machinery and illustrate an example of bond analysis on group 11 cyanides M–CN (M = Cu, Ag, Au).Chemistry is a visual discipline deeply relying on graphical representations for bringing the structure and behaviour of the microscopic world at the reach of our senses. Recent advances in computer graphics and the advent of immersive-virtual-reality technologies are creating great new opportunities in the way of conceiving these graphical representations and interacting with them. To seize these opportunities we have developed a virtual laboratory casting researchers amid the electron clouds of molecular systems and allowing them to perform a quantitative analysis of chemical bonding in an interactive and cooperative way. We discuss the developed machinery and illustrate an example of bond analysis on group 11 cyanides M–CN (M = Cu, Ag, Au).

Potential energy surfaces (PESs) for use in dynamics calculations of few-atom reactive systems are commonly modeled as functional forms fitting or interpolating a set of ab initio energies computed at many nuclear configurations. An automated procedure is here proposed for optimal configuration-space sampling in generating this set of energies as part of the grid-empowered molecular simulator GEMS (Laganà et al., J. Grid Comput. 2010, 8, 571-586). The scheme is based on a space-reduced formulation of the so-called bond-order variables allowing for a balanced representation of the attractive and repulsive regions of a diatom configuration space. Uniform grids based on space-reduced bond-order variables are proven to outperform those defined on the more conventional bond-length variables in converging the fitted/interpolated PES to the computed ab initio one with increasing number of grid points. Benchmarks are performed on the one- and three-dimensional prototype systems H2 and H3 using both a local-interpolation (modified Shepard) and a global-fitting (Aguado-Paniagua) scheme. Potential energy surfaces (PESs) for use in dynamics calculations of few atom reactive systems are commonly modeled as functional forms fitting or interpolating a set of ab initio energies computed at many nuclear configurations. An automated procedure is here proposed for optimal configuration-space sampling in generating this set of energies as part of the grid-empowered molecular simulator GEMS (Lagana et al., J. Grid Comput. 2010, 8, 571-586). The scheme is based on a space-reduced formulation of the so-called bond-order variables allowing for a balanced representation of the attractive and repulsive regions of a diatom configuration space. Uniform grids based on space-reduced bond-order variables are proven to outperform those defined on the more conventional bond-length variables in converging the fitted/interpolated PES to the computed ab initio one with increasing number of grid points. Benchmarks are performed on the one- and three-dimensional prototype systems H-2 and H-3 using both a local-interpolation (modified Shepard) and a global-fitting (Aguado-Paniagua) scheme.

open 12 si MIUR “PRIN 2015” funds (Grant Number 2015F59J3R) By combining rotational spectroscopy in supersonic expansion with the capability of state-of-the-art quantum-chemical computations in accurately determining structural and energetic properties, the genuine nature of a sulfur–sulfur chalcogen bond between dimethyl sulfide and sulfur dioxide has been unveiled in a gas-jet environment free from collision, solvent and matrix perturbations. A SAPT analysis pointed out that electrostatic S⋅⋅⋅S interactions play the dominant role in determining the stability of the complex, largely overcoming dispersion and C−H⋅⋅⋅O hydrogen-bond contributions. Indeed, in agreement with the analysis of the quadrupole-coupling constants and of the methyl internal rotation barrier, the NBO and NOCV/CD approaches show a marked charge transfer between the sulfur atoms. Based on the assignment of the rotational spectra for 7 isotopologues, an accurate semi-experimental equilibrium structure for the heavy-atom backbone of the molecular complex has been determined, which is characterized by a S⋅⋅⋅S distance (2.947(3) Å) well below the sum of van der Waals radii. embargoed_20191010 Obenchain, Daniel A.; Spada, Lorenzo; Alessandrini, Silvia; Rampino, Sergio; Herbers, Sven; Tasinato, Nicola; Mendolicchio, Marco; Kraus, Peter; Gauss, Jürgen; Puzzarini, Cristina; Grabow, Jens-Uwe*; Barone, Vincenzo Obenchain, Daniel A.; Spada, Lorenzo; Alessandrini, Silvia; Rampino, Sergio; Herbers, Sven; Tasinato, Nicola; Mendolicchio, Marco; Kraus, Peter; Gauss, Jürgen; Puzzarini, Cristina; Grabow, Jens-Uwe*; Barone, Vincenzo

We have recently introduced a simple yet powerful tool for analyzing quantitatively the coordination bond in terms of the donation and back-donation constituents of the Dewar-Chatt-Duncanson model. Our approach is based on the decomposition, via natural orbitals for chemical valence (NOCV), of the so-called charge-displacement (CD) function into additive chemically meaningful components (Bistoni et al. J. Chem. Phys. 2015, 142, 084112 ). The method, referred to as NOCV/CD, provides clear-cut measures of donation and back-donation charge flows following bond formation, and its robustness has been demonstrated by a tight correlation of the related charge-transfer estimates with experimental observables. In this paper we extend the NOCV/CD analysis scheme to the four-component relativistic framework, which includes spin-orbit coupling variationally. This formalism is incorporated into a recently developed, highly efficient parallel version of the relativistic Dirac-Kohn-Sham (DKS) program BERTHA (Rampino et al. J. Chem. Theory Comput. 2014, 10, 3766-3776 ). We test the accuracy and numerical stability of this new implementation through the analysis of the convergence properties of the basis sets employed to expand the DKS spinor solution and those used to linearize the electronic density in the density-fitting algorithm speeding up the evaluation of the DKS matrix. An illustration of NOCV/CD analysis in the relativistic framework is also given through a study of the metal-carbonyl coordination bond in a series of [M-CO]+ (M = Cu, Ag, Au) complexes of group 11 metals, where relativistic effects, including spin-orbit coupling, are found to play an important role.

The Grid Empowered Molecular Simulator GEMS enabling fully ab initio virtual experiments through rigorous theoretical and computational procedures has been upgraded with a novel scheme for automated generation of three-atom potential energy surfaces. The scheme is based on a space-reduced formulation of the so-called bond-order variables allowing for a balanced representation of the attractive and repulsive regions of a diatom configuration space. The deployment and use of the resulting upgraded machinery on distributed and cloud computing infrastructures is also discussed.

Thermal rate coefficients for the astrochemical reaction C + CH

Foundations and structure of the building blocks of GEMS, the ab initio molecular simulator designed for implementation on the EGEE computing Grid, are analyzed. The impact of the computational characteristics of the codes composing its blocks (the calculation of the ab initio potential energy values, the integration of the dynamics equations of the nuclear motion, and the statistical averaging of microscopic information to evaluate the relevant observable properties) on their Grid implementation when using rigorous ab initio quantum methods are discussed. The requests prompted by this approach for new computational developments are also examined by considering the present implementation of the simulator that is specialized in atom diatom reactive exchange processes. © 2010 Springer Science+Business Media B.V.

The detailed quantum probabilities of the O + O2 reactive system have been computed at zero total angular momentum using the time-independent quantum program ABC thanks to the restructuring of the code and its implementation on the EGEE production Grid. Their main features are discussed and out of them J-shifting thermal rate coefficients have been computed to compare with the experiment and quasiclassical trajectory results over a wide range of temperatures. © 2009 Springer-Verlag.

We performed a full coordinated run of the Grid-Empowered Molecular Simulator (GEMS) to the end of performing a dynamics investigation of the C (3P0) + CH+(X1σ+) →C2+(X4σg-) + H (2S1/2) reaction of astrochemistry relevance. The GEMS workflow allowed us to manage in a unified fashion the high-level ab initio calculation of the electronic structure of C2H+on an optimal space-reduced bond-order grid, the fitting of an accurate potential energy surface, the integration of quasiclassical dynamics equations for evaluating fully thermal and state-specific rate coefficients as well as more detailed dynamical properties by performing a massively distributed computational campaign of trajectory calculations. In this way we were able to check the validity of the formulation of the rate coefficient of the title reaction in popular astrochemistry databases, the dynamical nature of the temperature dependence of the rate coefficients, and the microscopic foundations of the branching mechanism of the reaction. Moreover, we checked the accuracy of our quasiclassical results against quantum calculations.

The CO stretching response upon coordination to a metal M to form [(L)(n)M(CO)](m) complexes (L is an auxiliary ligand) is investigated in relation to the sigma donation and pi back-donation components of the M-CO bond and to the electrostatic effect exerted by the ligand-metal fragment. Our analysis encompasses over 30 carbonyls, in which the relative importance of donation, back-donation and electrostatics are varied either through the ligand in a series of [(L)Au(CO)](0/+) gold(I) complexes, or through the metal in a series of anionic, neutral and cationic homoleptic carbonyls. Charge-displacement analysis is used to obtain well-defined, consistent measures of s donation and pi back-donation charges, as well as to quantify the sigma and pi components of CO polarization. It is found that all complexes feature a comparable charge flow of sigma symmetry (both in the M-CO bonding region and in the CO fragment itself), which is therefore largely uncorrelated to CO response. By contrast, pi back-donation is exceptionally variable and is found to correlate tightly with the change in CO bond distance, with the shift in CO stretching frequency, and with the extent and direction (C -> O or C

Thermal rate coefficients for the astrochemical reaction C + CH$^+$ $\to$ C$_2^+$ + H were computed in the temperature range 20-300 K by using novel rate theory based on ring polymer molecular dynamics (RPMD) on a recently published bond-order based potential energy surface and compared with previous Langevin capture model (LCM) and quasi-classical trajectory (QCT) calculations. Results show that there is a significant discrepancy between the RPMD rate coefficients and the previous theoretical results which can lead to overestimation of the rate coefficients for the title reaction by several orders of magnitude at very low temperatures. We argue that this can be attributed to a very challenging energy profile along the reaction coordinate for the title reaction, not taken into account in extenso by either the LCM or QCT approximation. In the absence of any rigorous quantum mechanical or experimental results, the computed RPMD rate coefficients represent state-of-the-art estimates to be included in astrochemical databases and kinetic networks.

The chemistry of superheavy elements (Z ≥ 104) is actively investigated in atom-at-a-time experiments of volatility through adsorption on gold surfaces. In this context, common guidelines for interpretation based on group trends in the periodic table should be used cautiously, because relativistic effects play a central role and may cause predictions to fall short. In this paper, we present an all-electron four-component Dirac-Kohn-Sham comparative study of the interaction of gold with Cn (Z = 112), Fl (Z = 114), and Uuo (Z = 118) versus their lighter homologues of the 6th period, Hg, Pb, and Rn plus the noble gas Xe. Calculations were carried out for Au-E (E = Hg, Cn, Pb, Fl, Xe, Rn, Uuo), Au7- and Au20-E (E = Hg, Cn, Pb, Fl, Rn) complexes, where Au7 (planar) and Au20 (pyramidal) are experimentally determined clusters having structures of increasing complexity. Results are analysed both in terms of the energetics of the complexes and of the electron charge rearrangement accompanying their formation. In line with the available experimental data, Cn and more markedly Fl are found to be less reactive than their lighter homologues. On the contrary, Uuo is found to be more reactive than Rn and Xe. Cn forms the weakest bond with the gold atom, compared to Fl and Uuo. The reactivity of Fl decreases with increasing gold-fragment size more rapidly than that of Cn and, as a consequence, the order of the reactivity of these two elements is inverted upon reaching the Au20-cluster adduct. Density difference maps between adducts and fragments reveal similarities in the behaviour of Cn and Xe, and in that of Uuo and the more reactive species Hg and Pb. These findings are given a quantitative ground via charge-displacement analysis.

Förster resonance energy transfer (FRET) is a key process in dyadic dye-sensitized solar cells (DSSCs) where an "antenna" donor has the role of collecting photons and redirecting the captured energy to an adsorbed-dye acceptor unit. Despite its popularity in, e.g., biology, where FRET rates are used to derive structural information on fairly complex systems, relatively few studies have appeared in the DSSCs field. These were based, to the best of our knowledge, either on a static modeling of FRET or on the so called isotropic regime assuming an isotropic motion of the donor/acceptor units and uncorrelated donor/acceptor relative distance and orientation. In this paper we carry out a combined Car-Parrinello molecular dynamics and TDDFT investigation to unravel the impact of thermal fluctuations on FRET in two dyadic carbazole-phenothiazine dye sensitizers. Both isolated and full-packed adsorption conditions are considered, mimicking the dye adsorption topology on TiO2. Results are discussed in relation to the above mentioned models and rationalized in terms of the structural differences of the considered dyes. We find a considerable difference between the FRET rates calculated at zero temperature and the results obtained by including thermal fluctuations, highlighting an important role of the latter in determining FRET rates in dyadic donor-acceptor dye-sensitized solar cells.

High level ab initio calculations have been carried out on an archetypal gold(I)-catalyzed reaction: hydroamination of ethyne. We studied up to 12 structures of possible gold(I)-coordinated species modeling different intermediates potentially present in a catalytic cycle for the addition of a protic nucleophile to an alkyne. The benchmark is used to evaluate the performances of some popular density functionals for describing geometries and relative energies of stationary points along the reaction profile. Most functionals (including hybrid or meta-hybrid) give accurate structures but large nonsystematic errors (4-12 kcal/mol) along the reaction energy profile. The double hybrid functional B2PLYP outperforms all considered functionals and compares very nicely with our reference ab initio benchmark energies. Moreover, we present an assessment of the accuracy of commonly used approaches to include relativistic effects, such as relativistic effective potentials and a scalar ZORA Hamiltonian, by a comparison with the results obtained using a relativistic all-electron four-component Dirac-Kohn-Sham method. The contribution of nonscalar relativistic effects in gold(I)-catalyzed reactions, as we investigated here, is expected to be on the order of 1 kcal/mol. © 2014 American Chemical Society.

We propose a new complete memory-distributed algorithm, which significantly improves the parallel implementation of the all-electron four-component Dirac-Kohn-Sham (DKS) module of BERTHA (J. Chem. Theory Comput. 2010, 6, 384). We devised an original procedure for mapping the DKS matrix between an efficient integral-driven distribution, guided by the structure of specific G-spinor basis sets and by density fitting algorithms, and the two-dimensional block-cyclic distribution scheme required by the ScaLAPACK library employed for the linear algebra operations. This implementation, because of the efficiency in the memory distribution, represents a leap forward in the applicability of the DKS procedure to arbitrarily large molecular systems and its porting on last-generation massively parallel systems. The performance of the code is illustrated by some test calculations on several gold clusters of increasing size. The DKS self-consistent procedure has been explicitly converged for two representative clusters, namely Au20 and Au34, for which the density of electronic states is reported and discussed. The largest gold cluster uses more than 39k basis functions and DKS matrices of the order of 23 GB. © 2013 American Chemical Society.

Golden fullerenes have recently been identified by photoelectron spectra by Bulusu et al. [S. Bulusu, X. Li, L.-S. Wang, X. C. Zeng, PNAS 2006, 103, 8326–8330]. These unique triangulations of a sphere are related to fullerene duals having exactly 12 vertices of degree five, and the icosahedral hollow gold cages previously postulated are related to the Goldberg–Coxeter transforms of C20starting from a triangulated surface (hexagonal lattice, dual of a graphene sheet). This also relates topologically the (chiral) gold nanowires observed to the (chiral) carbon nanotubes. In fact, the Mackay icosahedra well known in gold cluster chemistry are related topologically to the dual halma transforms of the smallest possible fullerene C20. The basic building block here is the (111) fcc sheet of bulk gold which is dual to graphene. Because of this interesting one-to-one relationship through Euler's polyhedral formula, there are as many golden fullerene isomers as there are fullerene isomers, with the number of isomers Nisoincreasing polynomially as (Formula presented.)). For the recently observed (Formula presented.), (Formula presented.), and (Formula presented.) we present simulated photoelectron spectra including all isomers. We also predict the photoelectron spectrum of (Formula presented.) . The stability of the golden fullerenes is discussed in relation with the more compact structures for the neutral and negatively charged Au12to Au20and Au32clusters. As for the compact gold clusters we observe a clear trend in stability of the hollow gold cages towards the (111) fcc sheet. The high stability of the (111) fcc sheet of gold compared to the bulk 3D structure explains the unusual stability of these hollow gold cages.

The quantum framework of the Grid Empowered Molecular Simulator GEMS has been assembled on the segment of the European Grid devoted to the Computational Chemistry Virtual Organization. The related grid based workflow allows the ab initio evaluation of the dynamics of small systems starting from the calculation of the electronic properties. Interoperability between computational codes across the different stages of the workflow was made possible by the use of the common data formats Q5Cost and D5Cost. Illustrative benchmark runs have been performed on the prototype H + H 2, N + N 2 and O + O 2 gas phase exchange reactions and thermal rate coefficients have been calculated for the last two. Results are discussed in terms of the modeling of the interaction and advantages of using the Grid is highlighted. © 2011 Elsevier B.V. All rights reserved.

Within the activities of the D37 COST Action, we have further developed the quantum dynamics framework of the grid empowered molecular simulator (GEMS) implemented on the segment of the European grid available to the COMPCHEM (computational chemistry) virtual organization. GEMS does now include in a full ab initio approach, the evaluation of the detailed quantum (both time dependent and time independent) dynamics of small systems starting from the calculation of the electronic structure properties as well as the direct calculation of thermalized properties. Illustrative, full dimensional applications of the extended simulator to the H + H 2, N + N 2, and O + O 2 systems are presented. © 2011 Wiley Periodicals, Inc.

The potential energy surface of the N + N2 atom diatom system has been reformulated using the LAGROBO functional form for interpolating ab initio points in the short distance region and using a modified Lennard Jones functional form to model the van der Waals interaction at long range. On the proposed surface extended quantum calculations have been performed using the European Grid platform. The values of the calculated thermal rate coefficients fairly reproduce the experimental results.

Grid empowered calculations are becoming an important advanced tool indispensable for scientific advances. The possibility of simplifying and harmonizing the work carried out by computational scientists using a Web Service approach is considered here. To this end, a new Collaborative Grid Framework has been developed and tested. As a study case a three dimensional reactive scattering code dealing with atom-diatom systems has been considered. To this end an extended study of the energy dependence of the electronically adiabatic reactivity of N + N2 has been performed on the EGEE Grid. © 2010 Elsevier B.V. All rights reserved.

State-to-state exact quantum probabilities of the N + N2exchange reaction have been calculated on the recently proposed L4 potential energy surface fitted to high level ab initio points using full-dimensional time-independent quantum techniques. Thermal rate coefficient values calculated on L4 were found not to differ from those calculated on a previously proposed potential energy surface. On the contrary, state-specific reaction probabilities calculated on the two surfaces are shown to differ significantly. Arguments for attributing the difference to specific features of the considered potential energy surfaces are provided. © 2009 the Owner Societies.

The atom-diatom time independent quantum reactive scattering program ABC implemented on the COMPCHEM section of the EGEE computing Grid has been used to compute isotope effects for the nitrogen atom - nitrogen molecule reactions. Exact J= 0 quantum scattering calculations were performed for both the 14N + 28N 2 and 14N + 30N 2 reactions on two different potential energy surfaces. Related reaction thresholds, reactive resonances and product distributions are discussed. J-shifting thermal rate coefficients are also calculated for a comparison with the experiment.

The Potential Energy Surface (PES) of the N + N 2 atom diatom system has been reformulated using the Largest Angle Generalisation of the Rotating Bond Order (LAGROBO) functional form for interpolating ab initio points in the short distance region and using a modified Lennard-Jones functional form to model the van der Waals interaction at long range. On the proposed surface extended quantum calculations have been performed using the Dynamics module of the Grid Empowered Molecular Simulator (GEMS) on the European Grid platform. The values of the calculated thermal rate coefficients fairly well reproduce the experimental results.

Zero total angular momentum exact quantum calculations of the probabilities of the N+N2 reaction have been performed on the L3 potential energy surface having a bent transition state. This has allowed us to work out J-shifting estimates of the thermal rate coefficient based on the calculation of either detailed (state-to-state) or cumulative (multiconfiguration) probabilities. The results obtained are used to compare the numerical outcomes and the concurrent computational machineries of both quantum and semiclassical approaches as well as to exploit the potentialities of the J-shifting model. The implications of moving the barrier to reaction from the previously proposed collinear geometry of the LEPS to the bent one of L3 are also investigated by comparing the related detailed reactive probabilities. © 2008 The Royal Swedish Academy of Sciences.

We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism. (C) 2015 AIP Publishing LLC.

Code interoperability and the search for domain-specific standard data formats represent critical issues in many areas of computational science. The advent of novel computing infrastructures such as computational grids and clouds make these issues even more urgent. The design and implementation of a common data format for quantum chemistry (QC) and quantum dynamics (QD) computer programs is discussed with reference to the research performed in the course of two Collaboration in Science and Technology Actions. The specific data models adopted, Q5Cost and D5Cost, are shown to work for a number of interoperating codes, regardless of the type and amount of information (small or large datasets) to be exchanged. The codes are either interfaced directly, or transfer data by means of wrappers; both types of data exchange are supported by the Q5/D5Cost library. Further, the exchange of data between QC and QD codes is addressed. As a proof of concept, the H + H2 reaction is discussed. The proposed scheme is shown to provide an excellent basis for cooperative code development, even across domain boundaries. Moreover, the scheme presented is found to be useful also as a production tool in the grid distributed computing environment. © 2013 Wiley Periodicals, Inc.