Automated software for counting and measuring Hyalella genus using artificial intelligence.

Amphipods belonging to the Hyalella genus are macroinvertebrates that inhabit aquatic environments. They are of particular interest in areas such as limnology and ecotoxicology, where data on the number of Hyalella individuals and their allometric measurements are used to assess the environmental dynamics of aquatic ecosystems. In this study, we introduce HyACS, a software tool that uses a model developed with the YOLOv3's architecture to detect individuals, and digital image processing techniques to extract morphological metrics of the Hyalella genus. The software detects body metrics of length, arc length, maximum width, eccentricity, perimeter, and area of Hyalella individuals, using basic imaging capture equipment. The performance metrics indicate that the model developed can achieve high prediction levels, with an accuracy above 90% for the correct identification of individuals. It can perform up to four times faster than traditional visual counting methods and provide precise morphological measurements of Hyalella individuals, which may improve further studies of the species populations and enhance their use as bioindicators of water quality.

Non-ergodic fragmentation upon collision-induced activation of cysteine-water cluster cations.

Cysteine-water cluster cations Cys(H2O)3,6+ and Cys(H2O)3,6H+ are assembled in He droplets and probed by tandem mass spectrometry with collision-induced activation. Benchmark experimental data for this biologically important system are complemented with theory to elucidate the details of the collision-induced activation process. Experimental energy thresholds for successive release of water are compared to water dissociation energies from DFT calculations showing that clusters do not only fragment exclusively by sequential emission of single water molecules but also by the release of small water clusters. Release of clustered water is observed also in the ADMP (atom centered density matrix propagation) molecular dynamics model of small Cys(H2O)3+ and Cys(H2O)3H+ clusters. For large clusters Cys(H2O)6+ and Cys(H2O)6H+ the less computationally demanding statistical Microcanonical Metropolis Monte-Carlo method (M3C) is used to model the experimental fragmentation patterns. We are able to detail the energy redistribution in clusters upon collision activation. In the present case, about two thirds of the collision energy redistribute via an ergodic process, while the remaining one third is transferred into a non-ergodic channel leading to ejection of a single water molecule from the cluster. In contrast to molecular fragmentation, which can be well described by statistical models, modelling of collision-induced activation of weakly bound clusters requires inclusion of non-ergodic processes.

Efecto de la deforestación ribereña sobre la materia orgánica particulada gruesa en quebradas con influencia ganadera de la región Andina de Colombia / Effect of riparian deforestation on coarse particulate organic matter in streams with livestock influence in the Andean region of Colombia

Introducción: La materia orgánica particulada gruesa originada en la vegetación ribereña es la fuente principal de energía en muchas cuencas de cabecera. Sin embargo, la transferencia de dicha materia es alterada por la destrucción de los bosques. Objetivo: Evaluar diferencias en la materia orgánica en quebradas con bosques y con pastizales. Métodos: Comparar las entradas, el almacenamiento y la exportación de esta materia orgánica en el cauce de quebradas con bosques y con pastizales, en la región central de los Andes de Colombia. En cada quebrada, se midieron los aportes verticales y laterales de hojarasca con canastas; hojarasca del lecho de las quebradas con cuadrantes, y la exportación de material con redes de deriva, con un alcance de 100 m. Resultados: Las quebradas con bosques ribereños recibieron un promedio anual de 915 g m-2 de materia orgánica particulada gruesa, exportando un total de 334 g m-3 y almacenando 732 g m-2, valores que fueron significativamente más altos que en quebradas con pastizales, donde los valores correspondientes fueron: 125.4 g m-2; 128 g m-3 y 205.5 g m-2. Conclusiones: La remoción de cobertura boscosa de la zona ribereña reduce la materia orgánica en estas cuencas de cabecera en Colombia.

Introduction: Coarse particulate organic matter originated in riparian vegetation is the main source of energy in many headwater streams. However, the transfer of such material is altered by the destruction of forests. Objective: To assess flow differences of this organic matter in streams with forests and grasslands. Methods: We compared input, storage and export of this organic matter in the riparian belts of streams with forests, and streams with grasslands, in the central Andean region of Colombia. For each stream, we measured vertical and lateral litter with baskets; stream bed litter with a quadrant, and matter export with drift nets, in a 100 m reach. Results: The streams with riparian forest received an average of 915 g m-2 of coarse particulate organic matter annually, exported a total of 334 g m-3 and stored 732 g m-2, values that were significantly higher than in grassland streams, where the corresponding values were: 125.4 g m-2; 128 g m-3 and 205.5 g m-2. Conclusions: The removal of tree cover from the riparian zone reduced the organic matter in these headwater streams of Colombia.

Altitudinal distribution of the functional feeding groups of aquatic macroinvertebrates using an ecological network in Andean streams / Distribución altitudinal de los grupos funcionales de alimentación de macroinvertebrados acuáticos utilizando una red ecológica en arroyos andinos

Abstract Introduction: Analysis of functional feeding groups (FFG) in aquatic macroinvertebrates is important in understanding the structure, function, and dynamics of ecological processes in ecosystems. Modularity refers to the degree of compartmentalization of food webs and varies between -1 and 1. A network with a modularity value close to 1 is resilient to disturbances and can be interpreted as an indicating factor for the stability of communities. Objective: In this study, we analyzed the trophic structure of benthic macroinvertebrates in La Nitrera stream, the San Juan River, and the Cauca River in the Colombian Andes. Methods: The study was supported by ecological networking techniques using Gephi software. We studied nine sites in dry, rainy, and transition seasons in 2017 and 2018, monitoring changes in the altitude gradient. At each of the sites, the organisms were captured and determined, and physicochemical and hydraulic information was obtained. Results: The variance component analysis allowed to explain the variability of the data by relating the following environmental variables: FFG, diversity, richness, modularity, season, and time. Simple multifactorial ANOVA indicated that significant changes in FFG were associated with altitude, and modularity to time. The allocation of the FFG was done by stomach analysis and secondary information. Conclusion: The transition season had the highest modularity, possibly due to the recolonization of some biotopes caused by the decrease in the velocity of water currents. La Nitrera and San Juan presented higher values than the Cauca, which may indicate that the altitudinal change and velocity of water currents affects the compartmentalization of the network.

Resumen Introducción: El análisis de grupos funcionales de alimentación (GFA) en macroinvertebrados acuáticos es importante para comprender la estructura, función y dinámica de los ecosistemas de procesos ecológicos. La modularidad se refiere al grado de compartimentación de las redes alimentarias y varía entre -1 y 1. Una red con un valor de modularidad cercano a 1 es resistente a las alteraciones y puede interpretarse como un factor indicativo para la estabilidad de las comunidades. Objetivo: En este estudio se analizó la estructura trófica de los macroinvertebrados bentónicos, un elemento importante en la calidad ambiental, en el arroyo La Nitrera, el río San Juan y el río Cauca. Métodos: El estudio contó con el apoyo de técnicas de redes ecológicas utilizando el software Gephi. En 2017 y 2018, estudiamos nueve sitios en estaciones secas, lluviosas y de transición, monitoreando cambios en el gradiente de altitud. En cada uno de los sitios se capturaron y determinaron los organismos y se recogió información fisicoquímica e hidráulica. Resultados: El análisis de componentes de varianza permitió explicar la variabilidad de los datos relacionando las siguientes variables ambientales: GFA, diversidad, riqueza, modularidad, estación y tiempo. La ANOVA simple multifactorial indicó que existen cambios significativos en los GFA en relación con la altitud, y la modularidad con el tiempo. La asignación de los GFA se realizó mediante análisis estomacal e información secundaria. Conclusión: La temporada de transición tuvo la mayor modularidad, posiblemente debido a la recolonización de algunos biotopos provocada por la disminución de la velocidad del cauce. La Nitrera y San Juan presentaron valores superiores a los del Cauca, lo que puede indicar que el cambio altitudinal y la velocidad de las corrientes de agua influyen en la compartimentación de la red.

A general approach to study molecular fragmentation and energy redistribution after an ionizing event.

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 photoelectron-photoion coincidence experiments and the different mass spectra obtained when ions ranging from Ar+ to Xe25+ 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.

SCC-DFTB Parameters for Fe-C Interactions.

We present an optimized density-functional tight-binding (DFTB) parameterization for iron-based complexes based on the popular trans3d set of parameters. The transferability of the original and optimized parameterizations is assessed using a set of 50 iron complexes, which include carbonyl, cyanide, polypyridine, and cyclometalated ligands. DFTB-optimized structures predicted using the trans3d parameters show a good agreement with both experimental crystal geometries and density functional theory (DFT)-optimized structures for Fe-N bond lengths. Conversely, Fe-C bond lengths are systematically overestimated. We improve the accuracy of Fe-C interactions by truncating the Fe-O repulsive potential and reparameterizing the Fe-C repulsive potential using a training set of six isolated iron complexes. The new trans3d*-LANLFeC parameter set can produce accurate Fe-C bond lengths in both geometry optimizations and molecular dynamics (MD) simulations, without significantly affecting the accuracy of Fe-N bond lengths. Moreover, the potential energy curves of Fe-C interactions are considerably improved. This improved parameterization may open the door to accurate MD simulations at the DFTB level of theory for large systems containing iron complexes, such as sensitizer-semiconductor assemblies in dye-sensitized solar cells, that are not easily accessible with DFT approaches because of the large number of atoms.

Methyl Paraben and Carbamazepine in Water and Striped Catfish (Pseudoplatystoma magdaleniatum) in the Cauca and Magdalena Rivers.

Between 2017 and 2019, samplings were carried out in the San Jorge, Cauca and Magdalena River basins in Colombia, to determine the presence of methyl paraben and carbamazepine in water and Pseudoplatystoma magdaleniatum. For the analysis of the samples, a validation of the analytical method was performed, following the EPA method 1694 (Pharmaceutical and personal care products in water), with slight modifications. This was done by liquid-chromatography tandem mass spectrometry, for quantification of methyl paraben and carbamazepine, including parameters of linearity, accuracy precision and veracity. Carbamazepine was found in the Magdalena River at 8.03 ± 0.01 µg/L in transition season. In fish samples, methyl paraben and carbamazepine were detected in a range between 32 and 90.80 µg/kg in transition and dry seasons.

Unraveling the structural stability and the electronic structure of ThO2 clusters.

Unraveling the correlations between the geometry, the relative energy and the electronic structure of metal oxide nanostructures is crucial for a better control of their size, shape and properties. In this work, we investigated these correlations for stoichiometric thorium dioxide clusters ranging from ThO2 to Th8O16 using a chemically-driven geometry search algorithm in combination with state-of-the-art first principles calculations. This strategy allows us to homogeneously screen the potential energy surface of actinide oxide clusters for the first time. It is found that the presence of peroxo and superoxo groups tends to increase the total energy of the system by at least 3.5 eV and 7 eV, respectively. For the larger clusters, the presence of terminal oxygen atoms increases the energy by about 0.5 eV. Regarding the electronic structure, it is found that the HOMO-LUMO gap is larger in systems containing only bridging oxygen atoms (∼2-3.5 eV) than for systems containing oxo groups (∼1-3 eV), peroxo groups (∼0-2 eV), and superoxo groups (∼0-1 eV). Furthermore, while the LUMO is always dominated by thorium orbitals, the composition of the HOMO changes in the presence or the absence of oxo, peroxo and/or superoxo groups: in the presence of peroxo groups, it is dominated by thorium orbitals, in all other cases, it is dominated by oxygen orbitals, and is rather localized in the presence of terminal oxo or superoxo groups. These correlations are of great interest for synthesizing clusters with tailored properties, especially for applications in the field of nuclear energy and heterogeneous catalysis.

Dissociation dynamics of the diamondoid adamantane upon photoionization by XUV femtosecond pulses.

This work presents a photodissociation study of the diamondoid adamantane using extreme ultraviolet femtosecond pulses. The fragmentation dynamics of the dication is unraveled by the use of advanced ion and electron spectroscopy giving access to the dissociation channels as well as their energetics. To get insight into the fragmentation dynamics, we use a theoretical approach combining potential energy surface determination, statistical fragmentation methods and molecular dynamics simulations. We demonstrate that the dissociation dynamics of adamantane dications takes place in a two-step process: barrierless cage opening followed by Coulomb repulsion-driven fragmentation.

Development of Density Functional Tight-Binding Parameters Using Relative Energy Fitting and Particle Swarm Optimization.

We provide a strategy to optimize density functional tight-binding (DFTB) parameterization for the calculation of the structures and properties of organic molecules consisting of hydrogen, carbon, nitrogen, and oxygen. We utilize an objective function based on similarity measurements and the Particle Swarm Optimization (PSO) method to find an optimal set of parameters. This objective function considers not only the common DFTB descriptors of binding energies and atomic forces but also incorporates relative energies of isomers into the fitting procedure for more chemistry-driven results. The quality in the description of the binding energies and atomic forces is measured based on the Ballester similarity index and relative energies through a similarity index induced by the Levenshtein edit distance to quantify the correct energetic order of isomers. Training and testing datasets were created to include all relevant chemical functional groups. The accuracy of this strategy is assessed, and its range of applicability is discussed by comparison against our previous parameterization [A. Krishnapriyan, et al., J. Chem. Theory Comput. 13, 6191 (2017)]. The improved performance of the new DFTB parameterization is validated with respect to the density functional theory large datasets QM-9 [R. Ramakrishnan, et al., Sci. Data 1, 140022 (2014)] and ANI-1 [J. S. Smith, et al., Sci. Data 4, 170193 (2017)], where excellent agreement is found between the structures and properties available in these datasets, and the ones obtained with DFTB.

Índice de Calidad Ecológica y gestión hídrica en tres ecosistemas de Colombia

Introducción: La investigación y el diagnóstico de fuentes hídricas es de interés académico y gubernamental, la exploración de instrumentos numéricos aplicados al ordenamiento de cuencas brinda la posibilidad de identificar dónde y qué variables son útiles en programas de monitoreo y rehabilitación en ecosistemas acuáticos, lo cual incluye la calidad del agua, convencionalmente analizada por índices fisicoquímicos e hidrobiológicos. En el 2014 a través de la guía de ordenamiento hídrico en Colombia, se desarrolló una evaluación del índice de calidad ecológica (ICE); la cual genera un sistema numérico de correlaciones que diagnostica, clasifica y detecta afectaciones ambientales. Objetivo: Esta investigación pretende demostrar que el ICE permite evaluar la calidad de ecosistemas acuáticos afectados por diferentes situaciones ambientales. Métodos: Se analizaron tres escenarios ubicados en diferentes regiones de Colombia y como grupo hidrobiológico indicador se utilizaron las algas perifíticas y fitoplanctónicas. Los ecosistemas fueron monitoreados entre el 2007 y 2016 y corresponden a una planicie de inundación, un río andino de alta montaña y un grupo de quebradas en un bosque húmedo tropical. Resultados: Las correlaciones canónicas fueron significativas (P < 0.005) y se estimó el óptimo y la tolerancia de cada taxa; variables relacionadas con la concentración de iones, la amortiguación de la acidez, la temperatura y la hidráulica, incidieron en la distribución de las abundancias de los organismos y la clasificación ecológica mediante el índice. Conclusiones: La aplicación del índice permite identificar variables, organismos y ordenamientos numéricos que posibilitan clasificar el estado ecológico en un sistema, resultados útiles en el diagnóstico y seguimiento de los ecosistemas acuáticos estudiados y que pueden ser implementados con otros escenarios.

Introduction: Research and diagnosis of water sources is of academic and governmental interest, for this reason, the exploration of numerical tools applied to watershed management, offers the possibility to identify where and what variables are useful in monitoring and rehabilitation programs of aquatic ecosystems. Environmental planning and management, which includes water quality, is conventionally analyzed by physical, chemical and hydrobiological indexes. In 2014, through the water management guide, included the assessment of the ecological quality index (EQI); it was generated a comprehensive approach through a numerical system of correlations that diagnoses, classifies and detects environmental impacts. Objective: This research aims to demonstrate that the EQI allows to assess the quality of aquatic ecosystems affected by different environmental situations. Methods: In order to analyze the application of this tool, we studied three scenarios located in different biogeographical regions of Colombia and, as a hydrobiological group indicator, we used peripheral and phytoplankton algae. The ecosystems were monitored between 2007 and 2015 and correspond to a flood plain, a high mountain Andean river and a group of water stream in a tropical humid forest. Results: Canonical correlations were significant (P < 0.005)and a model of weighted averages, allowed to estimate the optimum and the tolerance of each taxa for the sites ecological classification; variables related to ion concentration, acidity damping, temperature and hydraulics, influenced the models that explained the abundances distribution of the studied biological groups. Conclusions: The application of the EQI makes it possible to identify variables, organisms and numerical systems to classify ecological status. These results are useful in the diagnosis and monitoring of aquatic ecosystems and that can be implemented in other scenarios.

Fully versus constrained statistical fragmentation of carbon clusters and their heteronuclear derivatives.

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.

Evaluación de la exposición a campos electromagnéticos de radiofrecuencia en ámbitos académicos / Exposure assessment of radiofrecuency electromagnetic fields in academic areas

Introducción: Las radiaciones no ionizantes no poseen el nivel de energía requerido para producir ionización en los tejidos o causar daño al DNA, pero pueden generar efectos térmicos y no térmicos en la salud de los seres humanos que son actualmente motivo de estudio y discusión. Gran parte de la actividad cotidiana en ámbitos académicos se desarrolla bajo la influencia de innumerables radiaciones. Objetivo: Evaluar y determinar el nivel de exposición a las radiaciones no ionizantes en ámbitos académicos de la Universidad Nacional de La Plata, Argentina. Metodología: Las mediciones fueron realizadas mediante el instrumento marca Narda® NBM 550 con sonda de medición isotrópica en la banda de 100 kHz a 3 GHz. Se realizaron mediciones exteriores (outdoor) en diferentes facultades de la Universidad Nacional de La Plata. En la facultad de Ciencias Médicas se efectuaron mediciones interiores (indoor). En esta última se seleccionaron tres ambientes para determinar las principales fuentes de emisión. Resultados: Los valores máximos obtenidos de las mediciones se encontraron por debajo del valor máximo permitido de 0,2 mW/cm2. En la facultad de Ciencias Médicas se realizaron mediciones específicas en dos lugares de alto tránsito y uno de varias horas de permanencia en el lugar de exposición. El procesamiento de los datos reveló que las mediciones específicas a 20 cm de los artefactos eléctricos de iluminación fueron superiores al máximo permitido. Discusión: Si bien los resultados de las mediciones exteriores realizadas en los diversos ámbitos académicos se encuentran dentro de los valores permitidos, es recomendable que las mediciones se efectúen en forma anual, además de instalar fuentes de bajas emisiones

Introduction: Non-ionizing radiation does not have the level of energy required to produce ionization in tissues or cause DNA damage, but can generate thermal and non-thermal effects on human health that are currently the subject of study and discussion. Much of the daily activity in academic areas is performed under the influence of innumerable radiations. Objective: Evaluate the exposure levels to non-ionizing radiation in academic and sensitive areas in different faculties of the National University of La Plata, Argentina. Methodology: The measurements were made using the Narda® NBM 550 instrument with an isotropic measurement probe in the 100 kHz band at 3 GHz. Seven exterior measurements were taken (outdoor) in different Faculties: In the Faculty of Medical Sciences internal (indoor) measurements were made. Of the latter, three environments were selected to determine the main sources of emission. Results: The maximum values obtained from the external and internal measurements were found below the maximum value of 0.2 mW / cm2. At the Faculty of Medical Sciences, specific measurements were made on two sites of high circulation and on one of several hours of permanence at the place of exposure. Data processing revealed that the specific measurements at 20 cm of the electric lighting fixtures were higher than the maximum allowed. Discussion: It can be inferred that although the results of the external measurements made in the different academic fields are within the allowed values, it is recommended that the measurements be made annually and the use of low emission sources

Furan Fragmentation in the Gas Phase: New Insights from Statistical and Molecular Dynamics Calculations.

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 competition among them.

Extracellular enzymatic activity of two hydrolases in wastewater treatment for biological nutrient removal.

Due to the complex nature of the wastewater (both domestic and non-domestic) composition, biological processes are widely used to remove nutrients, such as carbon (C), nitrogen (N), and phosphorous (P), which cause instability and hence contribute to the damage of water bodies. Systems with different configurations have been developed (including anaerobic, anoxic, and aerobic conditions) for the joint removal of carbon, nitrogen, and phosphorus. The goal of this research is to evaluate the extracellular activity of ß-glucosidase and phosphatase enzymes in a University of Cape Town (UCT) system fed with two synthetic wastewaters of different molecular complexity. Both types of waters have medium strength characteristics similar to those of domestic wastewater with a mean C/N/P ratio of 100:13:1. The operation parameters were hydraulic retention time (HRT) of 10 h, solid retention time (SRT) of 12 days, mean concentration of the influent in terms of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) of 600, 80, and 6 mg/L, respectively. According to the results obtained, statistically significant differences have been found in the extracellular enzyme activities with the evaluated wastewaters and in the units comprising the treatment system in some of the cases. An analysis of principal components showed that the extracellular enzymatic activity has been correlated to nutrient concentration in wastewater, biomass concentration in the system, and metabolic conditions of treatment phases. Additionally, this research has allowed determining an inverse relationship between wastewater biodegradability and the extracellular enzyme activity of ß-glucosidase and phosphatase. These results highlight the importance of including the analysis of biomass biochemical characteristics as control methods in wastewater treatment systems for the nutrient removal.

M3C: A Computational Approach To Describe Statistical Fragmentation of Excited Molecules and Clusters.

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).

Structure, Ionization, and Fragmentation of Neutral and Positively Charged Hydrogenated Carbon Clusters: C(n)H(m)(q+) (n = 1-5, m = 1-4, q = 0-3).

In this work we present a systematic theoretical study of neutral and positively charged hydrogenated carbon clusters (C(n)H(m)(q+) with n = 1­5, m = 1­4, and q = 0­3). A large number of isomers and spin states (1490 in total) was investigated. For all of them, we optimized the geometry and computed the vibrational frequencies at the B3LYP/6-311++G(3df,2dp) level of theory; more accurate values of the electronic energy were obtained at the CCSD(T)/6-311++G(3df,2dp) level over the geometry previously obtained. From these simulations we evaluated several properties such as relative energies between isomers, adiabatic and vertical ionization potentials, and dissociation energies of several fragmentation channels. A new analysis technique is proposed to evaluate a large number of fragmentation channels in a wide energy range.

Communication: unraveling the (4)He droplet-mediated soft-landing from ab initio-assisted and time-resolved density functional simulations: Au@(4)He300/TiO2(110).

An ab-initio-based methodological scheme for He-surface interactions and zero-temperature time-dependent density functional theory for superfluid (4)He droplets motion are combined to follow the short-time collision dynamics of the Au@(4)He300 system with the TiO2(110) surface. This composite approach demonstrates the (4)He droplet-assisted sticking of the metal species to the surface at low landing energy (below 0.15 eV/atom), thus providing the first theoretical evidence of the experimentally observed (4)He droplet-mediated soft-landing deposition of metal nanoparticles on solid surfaces [Mozhayskiy et al., J. Chem. Phys. 127, 094701 (2007) and Loginov et al., J. Phys. Chem. A 115, 7199 (2011)].

Including nuclear quantum effects into highly correlated electronic structure calculations of weakly bound systems.

An interface between the APMO code and the electronic structure package MOLPRO is presented. The any particle molecular orbital APMO code [González et al., Int. J. Quantum Chem. 108, 1742 (2008)] implements the model where electrons and light nuclei are treated simultaneously at Hartree-Fock or second-order Möller-Plesset levels of theory. The APMO-MOLPRO interface allows to include high-level electronic correlation as implemented in the MOLPRO package and to describe nuclear quantum effects at Hartree-Fock level of theory with the APMO code. Different model systems illustrate the implementation: (4)He2 dimer as a protype of a weakly bound van der Waals system; isotopomers of [He-H-He](+) molecule as an example of a hydrogen bonded system; and molecular hydrogen to compare with very accurate non-Born-Oppenheimer calculations. The possible improvements and future developments are outlined.

Solvent states and spectroscopy of doped helium clusters as a quantum-chemistry-like problem.

The Full-Configuration-Interaction Nuclear-Orbital (FCI-NO) approach [J. Chem. Phys., 2009, 131, 19401], as the implementation of the quantum-chemistry ansatz, is overviewed and applied to (He)N-Cl2(X) clusters (N≤ 4). The ground and excited states of both fermionic (3)He and bosonic (4)He [see also, J. Phys. Chem. Lett., 2012, 2, 2145] clusters are studied. It is shown that the FCI-NO approach allows us to overcome three main difficulties: (1) the Fermi-Dirac (Bose-Einstein) nuclear statistics; (2) the wide (highly anharmonic) amplitudes of the He-dopant and He-He motions; and (3) both the weakly attractive (long-range) and the strongly repulsive (short-range) interaction between the helium atoms. Special emphasis is placed on the dependence of the cluster properties on the number of helium atoms, and on the comparison between the two helium isotopes. In particular, we analyze the analogies between quantum rings comprising electrons and (3)He atoms. The synthetic vibro-rotational Raman spectra of Cl2(X) immersed in ((3,4)He)N clusters (N≤ 4) are discussed as a function of the cluster size and the nuclear statistics. It is shown that the Coriolis couplings play a key role in modifying the spectral dopant profile in (3)He. Finally, we point out possible directions for future research using the quantum-chemistry ansatz.