Spin density distribution in open-shell transition metal systems: A comparative post-Hartree-Fock, Density Functional Theory and quantum Monte Carlo study of the CuCl2 molecule

We present a comparative study of the spatial distribution of the spin density (SD) of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wavefunction theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell of the copper atom and the delocalization of the 3d hole over the chlorine atoms. It is shown here that qualitatively different results for SD are obtained from these various quantum-chemical approaches. At the DFT level, the spin density distribution is directly related to the amount of Hartree-Fock exchange introduced in hybrid functionals. At the QMC level, Fixed-node Diffusion Monte Carlo (FN-DMC) results for SD are strongly dependent on the nodal structure of the trial wavefunction employed (here, Hartree-Fock or Kohn-Sham with a particular amount of HF exchange) : in the case of this open-shell system, the 3N -dimensional nodes are mainly determined by the 3-dimensional nodes of the singly occupied molecular orbital. Regarding wavefunction approaches, HF and CASSCF lead to strongly localized spin density on the copper atom, in sharp contrast with DFT. To get a more reliable description and shed some light on the connections between the various theoretical descriptions, Full CI-type (FCI) calculations are performed. To make them feasible for this case a perturbatively selected CI approach generating multi-determinantal expansions of reasonable size and a small tractable basis set are employed. Although semi-quantitative, these near-FCI calculations allow to clarify how the spin density distribution evolves upon inclusion of dynamic correlation effects. A plausible scenario about the nature of the SD is proposed.Comment: 13 pages, 12 Figure

Solving the CH4−_4^- riddle: the fundamental role of spin to explain metastable anionic methane

When atoms or molecules exist in the form of stable negative ions, they play a crucial role in the gas phase chemistry. Determining the existence of such an ion, its internal energy and its stability are necessary prerequisites to analyze the role of this ion in a particular medium. Experimental evidence of the existence of a negative methane ion CH$_4^-$ has been provided over a period of 50 years. However, quantum chemistry had not been able to explain its existence, and a detailed recent study has shown that the experimentally observed species cannot be described by the attachement of an electron in the ground state of CH$_4^-$. Here we describe CH$_4^-$ as being a metastable species in its lowest quartet spin state and we find that this species is a CH$_2^-$-:H$_2$ exciplex with three open shells, lying 5.8 eV above the methane singlet ground state but slightly below the dissociation fragments. The formation of charged exciplexes is a novel mechanism to explain small molecular anions with implications in a plethora of basic and applied research fields

Bond breaking and bond making in tetraoxygen: analysis of the O2(X3Sigma(g)-) + O2(X3Sigma(g)-) <==> O4 reaction using the electron pair localization function.

International audienceWe study the nature of the electron pairing at the most important critical points of the singlet potential energy surface of the 2O2 O4 reaction and its evolution along the reaction coordinate using the electron pair localization function (EPLF) [Scemama, A.; Chaquin, P.; Caffarel, M. J. Chem. Phys. 2004, 121, 1725]. To do that, the 3D topology of the EPLF calculated with quantum Monte Carlo (at both variational and fixed-node-diffusion Monte Carlo levels) using Hartree-Fock, multiconfigurational CASSCF, and explicitly correlated trial wave functions is analyzed. At the O4 equilibrium geometry the EPLF analysis reveals four equivalent covalent bonds and two lone pairs on each oxygen atom. Along the reaction path toward dissociation it is found that the two oxygen-oxygen bonds are not broken simultaneously but sequentially, and then the lone pairs are rearranged. In a more general perspective, the usefulness of the EPLF as a unique tool to analyze the topology of electron pairing in nontrivial chemical bonding situations as well as to visualize the major steps involved in chemical reactivity is emphasized. In contrast with most standard schemes to reveal electron localization (atoms in molecules, electron localization function, natural bond orbital, etc.), the newly introduced EPLF function gives a direct access to electron pairings in molecules

The lithium-thiophene interaction: a critical study using highly correlated electronic structure approaches of quantum chemistry

International audienceThe fundamental multicentric interaction of a lithium atom with a single thiophene ring is addressed. A systematic study of the interaction energy (IE) and geometry for the Li-T charge-transfer complex is done at the MP2 and CCSD(T) levels using increasingly large basis sets up to aug-cc-pVQZ (AVQZ). Basis set superposition errors (BSSE) are evaluated and shown to have a major impact on the value of the IE. The Fixed-Node Diffusion Monte Carlo (FN-DMC) method is used as an alternative basis-set-free approach to obtain what is likely to be the most accurate estimate of the IE obtained so far. While counterpoise-corrected MP2/AVQZ and CCSD(T)/AVTZ interaction energies are found to be −3.8 and −7.5 kcal/mol, the FN-DMC method yields +1.3 ± 1.7 kcal/mol. The slow convergence of the ab initio IE (and some key structural parameters) with respect to basis set quality and the discrepancy with the FN-DMC result is discussed. A visualization of the electron pairing using the electron pair localization function (EPLF) for the Li-doped versus undoped thiophene is also presented

Propuesta de política de gestión ambiental de la universidad católica de Trujillo- Benedicto Xvi, 2021-2024

La investigación tuvo como propósito elaborar una Propuesta de Política de Gestión Ambiental de la Universidad Católica de Trujillo Benedicto XVI, 2021-2024. Es una investigación de tipo básico, con enfoque cualitativo, método de investigación documental y diseño no experimental de corte transversal. La metodología empleada fue utilizar un análisis documental, analítico y sintético, para obtener y analizar datos. Asimismo, se utilizó el método inductivo puesto que permitió analizar las propuestas que han realizado otras universidades. Lo obtenido fue la situación de la gestión ambiental que posee la universidad y el diseño de la propuesta de la Política de Gestión Ambiental de la Universidad Católica de Trujillo Benedicto XVI, 2021-2024. Se concluyó que la propuesta de Política de Gestión Ambiental de la Universidad Católica de Trujillo Benedicto XVI, 2021-2024; abordo las dimensiones de Gestión Ambiental, Formación Universitaria, Investigación Universitaria, y Responsabilidad Social Universitaria; las cuales proponen un nuevo modelo institucional de gestión involucrada con sus compromisos ambientales para ser reconocida como una Universidad Ambientalmente Responsable y basada en el ciclo de la mejora continua. Palabra clave: Política; GestiTesi

Lie algebra on synchronization of different systems: a generalized function for Hodgkin-Huxley neurons

"In this contribution two results are taken: (1) The synchronization of noiseless Hodgkin- Huxley (HH) neurons is possible from robust feedback based on Lie algebra approaches and (2) the fact that, from Lie algebra of vector fields, the generalized synchronization of different (triangular form) chaotic systems can be used to derive an explicit synchronization function. Both results are extended to derive the synchronization function in HH neurons despite this systems are not in triangular form. Thus, the Lie algebra of vectors fields permits to establish a theoretical framework for finding the synchroniza- tion function in chaotic systems in face they have different model.

Una cartografía pictórica de 1730

El presente artículo expone los resultados preliminares de un análisis de imagen que pretende contribuir a despejar algunas incógnitas persistentes sobre la villa de las Aguas Calientes (Nueva España), haciendo uso de fuentes primarias escritas y gráficas, especialmente una cartografía pictórica de 1730. Los resultados muestran una imagen idealizada que confirma la idea de la invención del territorio como estrategia subjetiva.Este artigo apresenta os resultados preliminares da análise de imagem, que visa ajudar a dissipar algumas incertezas persistentes sobre a cidade de Aguas Calientes (Nova Espanha), utilizando fontes primárias pictórica e por escrito, especialmente no mapeamento pictórico da 1730. Os resultados mostram uma imagem idealizada que confirma a ideia da invenção do território como uma estratégia subjetiva.This paper presents the preliminary results of image analysis that aims to help clarify certain questions lingering on historiography of Villa of Aguas Calientes (New Spain), using primary written and graphic sources, especially a 1730 pictorial mapping. The text confirms the idea that the process of drawing territory, invents it as subjective strategy

Contribution of prosthetic treatment considerations for dental extractions of permanent teeth

Background. Tooth loss is an easily identifiable outcome that summarizes a complex suite of factors in an individual’s history of dental disease and its treatment by dental services over a lifetime. Assessment of overall tooth loss data is essential for epidemiologically evaluating the adequacy of dental care provided at a systems level, as well as for placing in context tooth loss for non-disease causes. For example, when derived from prosthetic treatment planning, the latter may unfortunately lead to some teeth being extracted (pulled) for the sake of better comprehensive clinical results. The objective of the present manuscript was to identify the contribution to overall tooth loss, by extraction of permanent teeth because of prosthetic treatment reasons. Material and Methods. A cross-sectional study included sex, age, total number of extractions performed by subject, sextant (anterior vs. posterior), group of teeth (incisors, canines, premolars and molars), upper or lower arch, and the main reason underlying extraction (extraction for any reason vs. prosthetic treatment), in patients 18 years of age and older seeking care at a dental school clinic in Mexico. A multivariate logistic regression model was generated. Results. A total of 749 teeth were extracted in 331 patients; 161 teeth (21.5% of total) were extracted for explicit prosthetic treatment indications. As age increased, the likelihood of having an extraction for prosthetic reasons increased 3% (OR = 1.03, p < 0.001). Women (OR = 1.57, p < 0.05) were more likely to be in this situation, and molars (OR = 2.70, p < 0.001) were most at risk. As the total number of extractions increased, the risk of having an extraction for prosthetic reasons decreased (OR = 0.94, p < 0.05). Conclusions. A significant amount (21.5%) of the extractions of permanent teeth were performed for prosthetic reasons in this dental school clinical environment; age, sex, type of tooth, and the total number of extractions moderated such pattern

¿Cómo se discute la violencia contra las mujeres en el espacio público digital?: divulgación de resultados investigación-docencia

Este documento presenta los resultados más relevantes de un proceso de investigación y docencia desarrollado en el marco de los cursos C-1103 Comunicación y Poder y C-1002 Comunicación Inclusiva de la Concentración en Comunicación Social de la Escuela de Ciencias de la Comunicación Colectiva durante el ciclo II-2020, en articulación con el Programa de Narrativas, Género y Comunicación del Centro de Investigación en Comunicación – CICOM-, de la Universidad de Costa Rica (UCR). El proyecto se planteó objetivos en tres ámbitos: el de la investigación, el de la enseñanza-aprendizaje y el de la política pública. En primer lugar, esta investigación responde al esfuerzo de articulación entre el CICOM y el Instituto Nacional de las Mujeres, INAMU, institución que coordina a las 22 instituciones que conforman el Sistema Nacional de prevención y atención de la violencia contra las mujeres e intrafamiliar (Ley 8688), encargado de implementar la Política Nacional para la atención y prevención de la violencia contra las mujeres de todas las edades, PLANOVI 2017-2032 y del cual la UCR es parte. Esta política, particularmente los ejes 1 y 2, centran su interés en la comunicación como vehículo fundamental para conseguir el cambio cultural y propiciar la erradicación de la violencia contra las mujeres y la promoción de las masculinidades no violentas. Para ello, se requiere diseñar e implementar una estrategia integrada de comunicación que exige, como punto de partida, determinar cuáles son los discursos sobre la violencia contra las mujeres que circulan en el espacio público costarricense en la actualidad. Con este documento, aspiramos a generar insumos que impacten en el diseño de dicha estrategia.Universidad de Costa Rica/[]/UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Sociales::Centro de Investigación en Comunicación (CICOM