[Barrier dysfunction and Guillain-Barre syndrome as exponents of endothelial damage in COVID-19]. / Disfunción de barrera y síndrome de Guillain-Barré como exponentes del daño endotelial en la COVID-19.

TITLE: Disfunción de barrera y síndrome de Guillain-Barré como exponentes del daño endotelial en la COVID-19.

[Oxidative stress and epigenetics in obesity, metabolic syndrome and olfactory perception]. / Estrés oxidativo y epigenética en la obesidad, el síndrome metabólico y la percepción olfativa.

TITLE: Estrés oxidativo y epigenética en la obesidad, el síndrome metabólico y la percepción olfativa.

[New evidence and challenges on chronic relapsing inflammatory optic neuropathy]. / Nuevas evidencias y retos sobre neuropatia optica inflamatoria recurrente cronica.

TITLE: Nuevas evidencias y retos sobre neuropatia optica inflamatoria recurrente cronica.

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

Most ab initio calculations on fullerene molecules have been carried out on the basis of the paradigm of the Hückel model. This is consistent with the restricted nature of the independent-particle model underlying such calculations, even in single-reference-based correlated approaches. Notwithstanding, previous works on some of these molecules using model Hamiltonians have clearly indicated the importance of short-range interatomic spin-spin correlations. In this work, we consider ab initio non-collinear Hartree-Fock (HF) solutions for representative fullerene systems: the bowl, cage, ring, and pentagon isomers of C20, and the larger C30, C36, C60, C70, and C84 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 π-electron space becoming polyradical in nature: each p-orbital remains effectively singly occupied. The spin frustration, induced by the presence of pentagon rings on an otherwise antiferromagnetic background, is minimized at the HF level by aligning the spins with non-collinear arrangements. The long-range magnetic ordering observed is reminiscent of the character of broken symmetry HF solutions in polyacene systems.

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(µ-oxo) forms of [Cu2O2](2+), comparable to other state-of-the-art quantum chemical methods.

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 C2 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 C2v insertion pathway for BeH2. 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.

Unveiling the origin of shape coexistence in lead isotopes.

Shape coexistence in the nuclei (182-192)Pb is analyzed with the Hartree-Fock-Bogoliubov approach and the Gogny force. Good agreement with the experimental energies is found for the coexisting spherical, oblate, and prolate states. Contrary to the established interpretation, it is found that the low-lying prolate and oblate 0+ states are predominantly characterized by neutron correlations whereas the protons behave, in general, rather as spectators than playing an active role.