Álvaro Valdés

A CCSD(T)/CBS machine-learning potential energy surface and MCTDH quantum calculations reveal the strongly anharmonic vibrational structure of the proton-bound mixed noble-gas complex [Ar–H–He] ⁺ , providing new spectroscopic benchmarks.

Motivated by two of the most unexpected discoveries in recent years - the detection of ArH+ and HeH+ noble gas molecules in the cold, low-pressure regions of the Universe - we investigate [He2H]+ and [Ne2H]+ as potentially detectable species in the interstellar medium, providing new insights into their energetic and spectral properties. These findings are crucial for advancing our understanding of noble gas chemistry in astrophysical environments. To achieve this, we employed a data-driven approach to construct a high-accuracy, machine-learning potential energy surface (ML-PES) using the reproducing kernel Hilbert space (RKHS) method. Training and testing datasets are generated via high-level CCSD(T)/CBS[56] quantum chemistry computations, followed by a rigorous validation protocol to ensure the reliability of the potential. The ML-PES is then used to compute vibrational states within the MCTDH framework, and assign spectral transitions for the most common isotopologues of these species in the interstellar medium. Our results compared with previously recorded values, revealing that both cations exhibit a prominent proton-shuttle motion within the infrred spectral range, making them strong candidates for telescopic observation. This study provides a solid computational foundation, based on rigorous fully quantum treatments, aiming to assist in the identification of these yet unobserved He/Ne hydride cations in astrophysical environments.

We present new results on the underlying guest–host interactions and spectral characterization of a CO2 molecule confined in the cages of the sI clathrate hydrate. Such types of porous solids raise computational challenges, as they are of practical interest as gas storage/capture materials. Accordingly, we have directed our efforts toward addressing their modeling in a proper manner, ensuring the quality of the input data and the efficiency of the computational approaches. The computational procedure for spectral simulations, within the multi-configurational time-dependent Hartree framework, involves the development of a fully coupled Hamiltonian, including an exact kinetic energy operator and a many-body representation of the potential, along with dipole moment surfaces, both obtained through neural network machine learning techniques. The resulting models were automatically trained and tested on extensive datasets generated by PW86PBE-XDM calculations, following the outcome of previous benchmark studies. Our simulations enable us to explore various aspects of the quantized dynamics upon confinement of CO2@D/T, such as constrained rotational–translational quantum motions and the averaged position/orientation of the CO2 guest in comparison to the experimental data available. Particularly notable are the distinct energy patterns observed in the computed spectra for the confined CO2 in the D and T cages, with a considerably high rotational–translational coupling in the CO2@T case. Leveraging reliable computations has proved instrumental, highlighting the sensitivity of the spectral features to the shape and strength of the potential interactions, with the explicit description of many-body contributions being significant.

One of the most fascinating discoveries in the last years, in the cold and low pressure regions of the Universe, was the detection of the ArH⁺ and HeH⁺ species. The identifcation of such noble gas- containing molecules in the space is the key to understand the noble gas chemistry. In the present work, we discuss the possibility of the Ar₂H⁺ existence as a potentially detectable molecule in the interstellar medium, providing new data on possible astronomical pathways and energetics of such compound. As a first step, a data driven approach is proposed to construct a full 3D machine-learning potential energy surface via the reproducing kernel Hilbert space method. The training and testing data sets are generated from CCSD(T)/CBS[56] computations, while a validation protocol is introduced to ensure the quality of the potential. In turn, the resulting potential is employed to compute vibrational levels and molecular spectroscopic constants for the cation. In that way, the most common isotopologue in the ISM, ³⁶Ar₂H⁺, has been characterized for the first time, while simultaneously, comparisons with previously reported values available for the ⁴⁰Ar₂H⁺ are discussed. Our present data could serve as a benchmark for future studies on this system, as well as on higher-order cationic Ar hydrides of astrophysical interest.

A water molecule confined inside the C₇₀ fullerene was quantum‐mechanically described using a computational approach within the MCTDH framework. Such procedure involves the development of a full‐dimensional coupled hamiltonian, with an exact kinetic energy operator, including all rotational, translational and vibrational degrees of freedom of the endofullerene system. In turn, through an effective pairwise potential model, the ground and rotationally excited states of the encapsulated H₂O inside the C₇₀ cage were calculated, and traced back to the isotropic case of the H₂O@C₆₀ endofullerene in order to understand the nature and physical origin of the symmetry breaking observed experimentally in the latter system. Moreover, the computational scheme used here allows to study the quantization of the translational movement of the encapsulated water molecule inside the C₇₀ fullerene, and to investigate the confinement effects in the vibrational energy levels of the H₂O@C₇₀ system.

The National University of Colombia boasts a clear and egalitarian salary regime for its academic staff. Apart from rules concerning maternity and paternity leaves, which follow national Colombian legislation, the Academic Personal Statute is completely free of gender-based norms. Salaries are assigned through a points system that considers training level, productivity, and academic rank. With this in mind, one might expect to find egalitarian male and female salary conditions free of the gender-related gaps existing in other, more arbitrary private work environments. In this article, we present the results of a variance decomposition analysis of the gross salaries of all full-time professors and report the existence of an unadjusted gender pay gap of 0.12 and adjusted or unexplained gaps of 0.07-0.09 obtained through a Mincer earnings regression and a Blinder-Oaxaca decomposition. Partial correlations between these gaps and the different factors that come into play are examined and analyzed. The high impact of professors’ research track record on their salaries appears as the main contribution to the gender differences. It seems plausible that the crucial need for time to dedicate to research opens the window to the patriarchal society to permeate the otherwise egalitarian salary regime of the University, especially for the highest range of salaries corresponding mainly to male full professors who are very active in research.

The formation of specific clathrate hydrates and their transformation at given thermodynamic conditions depends on the interactions between the guest molecule/s and the host water lattice. Understanding their structural stability is essential to control structure‐property relations involved in different technological applications. Thus, the energetic aspects relative to CO₂@sI clathrate hydrate are investigated through the computation of the underlying interactions, dominated by hydrogen bonds and van der Waals forces, from first‐principles electronic structure approaches. The stability of the CO₂@sI clathrate is evaluated by combining bottom‐up and top‐down approaches. Guest‐free and CO₂ guest‐filled aperiodic cages, up to the gradually CO₂ occupation of the entire sI periodic unit cells were considered. Saturation, cohesive and binding energies for the systems are determined by employing a variety of density functionals and their performance is assessed. The dispersion corrections on the non‐covalent interactions are found to be important in the stabilization of the CO₂@sI energies, with the encapsulation of the CO₂ into guest‐free/empty cage/lattice being always an energetically favorable process for most of the functionals studied. The PW86PBE functional with XDM or D3(BJ) dispersion corrections predicts a lattice constant in accord to the experimental values available, and simultaneously provides a reliable description for the guest‐host interactions in the periodic CO₂@sI crystal, as well as the energetics of its progressive single cage occupancy process. It has been found that the preferential orientation of the single CO₂ in the large sI crystal cages has a stabilizing effect on the hydrate, concluding that the CO₂@sI structure is favored either by considering the individual building block cages or the complete sI unit cell crystal. Such benchmark and methodology cross‐check studies benefit new data‐driven model research by providing high‐quality training information, with new insights that indicate the underlying factors governing their structure‐driven stability, and triggering further investigations for controlling the stabilization of these promising long‐term CO₂ storage materials.