Polyradical character and spin frustration in fullerene molecules: An ab initio non-collinear Hartree--Fock study

Most {\em ab initio} calculations on fullerene molecules have been carried out based on the paradigm of the H\"uckel model. This is consistent with the restricted nature of the independent-particle model underlying such calculations, even in single-reference-based correlated approaches. On the other hand, previous works on some of these molecules using model Hamiltonians have clearly indicated the importance of short-range inter-atomic spin-spin correlations. In this work, we consider {\em ab initio} non-collinear Hartree--Fock (HF) solutions for representative fullerene systems: the bowl, cage, ring, and pentagon isomers of C$_{20}$, and the larger C$_{30}$, C$_{36}$, C$_{60}$, C$_{70}$, and C$_{84}$ fullerene cages. In all cases but the ring we find that the HF minimum corresponds to a truly non-collinear solution with a torsional spin density wave. Optimized geometries at the generalized HF (GHF) level lead to fully symmetric structures, even in those cases where Jahn-Teller distortions have been previously considered. The nature of the GHF solutions is consistent with the $\pi$-electron space becoming polyradical in nature: each $p$-orbital remains effectively singly occupied. The spin frustration, induced by the pentagon rings in an otherwise anti-ferromagnetic background, is minimized at the HF level by aligning the spins in non-collinear arrangements. The long-range magnetic ordering observed is reminiscent of the character of broken symmetry HF solutions in polyacene systems.Comment: 16 figure

Multi-reference symmetry-projected variational approximation for the ground state of the doped one-dimensional Hubbard model

A multi-reference configuration mixing scheme is used to describe the ground state, characterized by well defined spin and space group symmetry quantum numbers as well as doping fractions $N_{e}/N_{sites}$, of one dimensional Hubbard lattices with nearest-neighbor hopping and periodic boundary conditions. Within this scheme, each ground state is expanded in a given number of nonorthogonal and variationally determined symmetry-projected configurations. The results obtained for the ground state and correlation energies of half-filled and doped lattices with 30, 34 and 50 sites, compare well with the exact Lieb-Wu solutions as well as with the ones obtained with other state-of-the-art approximations. The structure of the intrinsic symmetry-broken determinants resulting from the variational procedure is interpreted in terms of solitons whose translational and breathing motions can be regarded as basic units of quantum fluctuations. It is also shown that in the case of doped 1D lattices, a part of such fluctuations can also be interpreted in terms of polarons. In addition to momentum distributions, both spin-spin and density-density correlation functions are studied as functions of doping. The spectral functions and density of states, computed with an ansatz whose quality can be well-controlled by the number of symmetry-projected configurations used to approximate the $N_{e} \pm 1$ electron systems, display features beyond a simple quasiparticle distribution, as well as spin-charge separation trends.Comment: 16 pages, 11 figure

Excited electronic states from a variational approach based on symmetry-projected Hartree--Fock configurations

Recent work from our research group has demonstrated that symmetry-projected Hartree--Fock (HF) methods provide a compact representation of molecular ground state wavefunctions based on a superposition of non-orthogonal Slater determinants. The symmetry-projected ansatz can account for static correlations in a computationally efficient way. Here we present a variational extension of this methodology applicable to excited states of the same symmetry as the ground state. Benchmark calculations on the C$_2$ dimer with a modest basis set, which allows comparison with full configuration interaction results, indicate that this extension provides a high quality description of the low-lying spectrum for the entire dissociation profile. We apply the same methodology to obtain the full low-lying vertical excitation spectrum of formaldehyde, in good agreement with available theoretical and experimental data, as well as to a challenging model $C_{2v}$ insertion pathway for BeH$_2$. The variational excited state methodology developed in this work has two remarkable traits: it is fully black-box and will be applicable to fairly large systems thanks to its mean-field computational cost

Multi-component symmetry-projected approach for molecular ground state correlations

The symmetry-projected Hartree--Fock ansatz for the electronic structure problem can efficiently account for static correlation in molecules, yet it is often unable to describe dynamic correlation in a balanced manner. Here, we consider a multi-component, systematically-improvable approach, that accounts for all ground state correlations. Our approach is based on linear combinations of symmetry-projected configurations built out of a set of non-orthogonal, variationally optimized determinants. The resulting wavefunction preserves the symmetries of the original Hamiltonian even though it is written as a superposition of deformed (broken-symmetry) determinants. We show how short expansions of this kind can provide a very accurate description of the electronic structure of simple chemical systems such as the nitrogen and the water molecules, along the entire dissociation profile. In addition, we apply this multi-component symmetry-projected approach to provide an accurate interconversion profile among the peroxo and bis($\mu$-oxo) forms of [Cu$_2$O$_2$]$^{2+}$, comparable to other state-of-the-art quantum chemical methods

Quality Control of the Thermal Properties of Superstructures in Accommodation Spaces in Naval Constructions

The application of passive design strategies in ships, such as the use of superstructures with high thermal insulation, allows the energy demand of heating, ventilation, and air conditioning systems to be reduced. There is a knowledge gap in the scientific literature on the possibilities to thermally characterize superstructures. Knowing such possibilities would make a methodology available for the quality control of naval constructions and for the inspection of the appropriate state of insulations in existing ships. For this purpose, a total of three different typologies of ship superstructures were monitored, and the data obtained were analyzed by using various existing approaches for the thermal characterization of facades: the heat flow meter method and temperature measurement methods. The results showed that the heat flow meter method constitutes a valid methodology to obtain representative results. In addition, guaranteeing a thermal gradient dependent of the wall typology and placing probes in zones not influenced by thermal bridges ensure that representative results are achieved

La eficacia a largo plazo de un programa de intervención basada en la atención plena (MBI) para la tartamudez: un estudio de caso

A mindfulness-based intervention (MBI) to address emotional factors that may negatively impact the fluency of the subjects was implemented. A MBI consisting of 5 weekly 2-h sessions was designed and applied to two stuttering cases. The goals were to lower stuttering and to reduce anxiety through the acquisition of mindfulness skills. Participants were asked to video-record a speaking task and to fill out anxiety and mindfulness skills self-reports pre and post-intervention. Both participants diminished stuttering error rates from severe (participant 1) and moderate (participant 2) to mild. Participant 2, who showed high pre-treatment anxiety, showed a significant reduction. A year-follow-up revealed that therapeutic gains in anxiety, mindfulness skills, and stuttering were successfully maintained in both participants. This is the first study focused on emotional aspects of stuttering showing long-term improvements through a MBI. MBI programs could serve as a promising complement for stuttering treatments.Se utilizó una intervención basada en mindfulness (MBI) para abordar los factores emocionales que pueden afectar negativamente a la fluidez de los sujetos a través de un estudio de caso. Se diseñó un MBI que constaba de 5 sesiones semanales de 2 horas y se aplicó a dos casos de tartamudez. Los objetivos eran dismunuir la tartamudez y reducir los síntomas de ansiedad mediante la adquisición de habilidades de atención plena. Se pidió a los participantes que grabaran en video una tarea oral y que cumplimentaran los autoinformes de ansiedad y de habilidades de atención plena antes y después de la intervención. En ambos participantes disminuyó el índice de errores de tartamudeo de grave (participante 1) y moderado (participante 2) a leve. El participante 2, que mostró una elevada ansiedad previa al tratamiento, mostró una reducción significativa. Al año de seguimiento los beneficios terapéuticos en ansiedad, habilidades de atención plena y tartamudeo se mantuvieron con éxito en ambos participantes. Se trata del primer estudio centrado en los aspectos emocionales de la tartamudez que muestra mejoras a largo plazo a través de un MBI. Por lo tanto, los programas MBI podrían servir como complemento prometedor a los tratamientos de tartamudezJennifer E. Moreno-Jiménez was granted a predoctoral fellowship, FPI-UAM 2017 of the Universidad Autónoma de Madri

Taxonomy of defects in auxiliary elements of facades and its relation with lawsuits filed by property owners

While at first it can be thought that the auxiliary elements of facades are merely ornamental with little practical function, this study shows that these components of the building envelope have a high impact on the envelope"s functioning and performance. This is carried out through the analysis of all relevant lawsuits filed in Spain over a 10 year period, a data set in which a surprisingly high number of 1033 cases of defects was found to affect external windowsills, exterior wainscots or cornices (the three auxiliary elements considered) was found. Considering the total number of lawsuits, this is an objectively unprecedented study. An analysis is carried out regarding the interrelations between elements, defects, causes, and types of buildings, with the aim of obtaining a sorted classification of the data. This constitutes a useful tool to prevent future problems arising from either the design, execution, or maintenance of facades. These include various issues resulting from humidities, one of the most frequent envelope defects, which are found to significantly affect the auxiliary elements of facades.Se trata de un estudio del número total de demandas de daños en fachadas durante 10 años, objetivamente sin precedentes. Se realiza un análisis de las interrelaciones entre elementos, defectos, causas y tipos de edificaciones, con el objetivo de obtener una clasificación ordenada de los datos. Esto constituye una herramienta útil para prevenir futuros problemas derivados del diseño, ejecución o mantenimiento de fachadas

Procedimiento de obtención de partículas de ZnO con morfología acicular

Referencia OEPM: P200001597.-- Fecha de solicitud: 27/06/2000.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento de obtención de partículas de ZnO con morfología acicular. La presente invención utiliza el método de precipitación controlada para obtener partículas de ZnO con morfología acicular. A través del control de los parámetros de formación de precursores intermedios de compuestos de cinc y la evolución de dichos precursores intermedios mediante el lavado con agua destilada de la suspensión coloidal se obtiene hidróxido de cinc. La destilación entre 100-150°C de una suspensión acuosa del hidróxido de zinc produce la formación de partículas de óxido de cinc con morfología acicular. El tamaño de las partículas varía con las condiciones de obtención, siendo el tamaño estándar de 0.5 μm de diámetro y 5-8 μm de longitud. La eficacia del procedimiento es superior al 90%.Peer reviewe

A Network Analysis of the Five Facets Mindfulness Questionnaire (FFMQ)

Objectives: The Five Facet Mindfulness Questionnaire (FFMQ) is a popular self-report instrument for mindfulness assessment. However, several studies report mixed evidence regarding its reliability and validity. While recent replication studies have shown several issues regarding its latent structure, first-order facets seemed to replicate successfully. This study proposes an exploratory approach to these facets on an item level in one sample, with cross-validation in another sample. Methods: Using a snowball sampling, 1008 participants were recruited in the first sample. Psychometric networks were applied to explore relations between items and item clusters. We compared these exploratory latent variable proposals with previous literature. A second sample of 1210 participants was collected from an FFMQ validation study, and confirmatory factor analyses were applied to cross-validate findings on the first sample. Results: The FFMQ showed a positively correlated network. Exploratory analyses suggested the 5-facet structure as stable with alternatives of 4-facet (merging Observe and Non-Judging) and 6-facet (splitting Acting with Awareness in two) solutions. However, the CFAs in the second sample did not provide clear support to any solution. Conclusions: The FFMQ showed unclear evidence on its latent structure. We propose researchers and users of the FFMQ to use the most fitting solution between the 5 and 6-facet solutions in their data, since the 4-facet solution is difficult to interpret. We also propose cautionary notes and guidelines for researchers and applied users of the FFMQ and regarding this instrument. We conclude that more research is needed in mindfulness assessment to provide robust measurement