arXiv subjects

Francesc Illas

Publications and source records attributed to Francesc Illas.

4 recordsLinked to original sources

arXiv2025

Tuning topologically nontrivial states in the BHT-Ni metal organic framework

Using first principles calculations, we have demonstrated the creation of multiple quantum states, in the experimentally accessible metal organic framework BHT-Ni. Specifically, quantum spin Hall and quantum anomalous Hall states are induced by two and four electron doping, respectively. The geometrical symmetry breaking, is also investigated. For a low electron doping concentration of two electrons per unit cell, the Fermi energy shifts to a nontrivial band gap, between Dirac bands and a quantized spin Hall conductivity is predicted. Subsequently in a high electron doping concentration, Anomalous Hall conductivity with a quantized value was observed. In addition, for centrosymmetric (trans-like) and non-centrosymmetric (cis-like) structures, we found that the trans-like structure preserves quantum spin Hall and quantized spin Hall conductivity. In contrast, in the cis-like structure, space inversion symmetry breaking leads to the appearance of valley Hall effect and the disappearance of spin Hall conductivity.

cond-mat.mtrl-sci↗

arXiv2022

Artifcial-intelligence-driven discovery of catalyst \textit{genes} with application to CO2 activation on semiconductor oxides

Catalytic-materials design requires predictive modeling of the interaction between catalyst and reactants. This is challenging due to the complexity and diversity of structure-property relationships across the chemical space. Here, we report a strategy for a rational design of catalytic materials using the artifcial intelligence approach (AI) subgroup discovery. We identify catalyst \textit{genes} (features) that correlate with mechanisms that trigger, facilitate, or hinder the activation of carbon dioxide (CO$_2$) towards a chemical conversion. The AI model is trained on frst-principles data for a broad family of oxides. We demonstrate that surfaces of experimentally identifed good catalysts consistently exhibit combinations of \textit{genes} resulting in a strong elongation of a C-O bond. The same combinations of \textit{genes} also minimize the OCO-angle, the previously proposed indicator of activation, albeit under the constraint that the Sabatier principle is satisfed. Based on these fndings, we propose a set of new promising catalyst materials for CO$_2$ conversion.

cond-mat.mtrl-sci↗

arXiv2003

The role of dynamical polarization of the ligand to metal charge transfer excitations in {\em ab initio} determination of effective exchange parameters

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits to suggest a new variant of the Difference Dedicated Configuration Interaction (DDCI) method, presently one of the most accurate and reliable for the evaluation of magnetic effective interactions. This new method treats the bridging ligand orbitals mediating the interaction at the same level than the magnetic orbitals and preserves the high quality of the DDCI results while being much less computationally demanding. The numerical accuracy of the new approach is illustrated on various systems with one or two magnetic electrons per magnetic center. The fact that accurate results can be obtained using a rather reduced configuration interaction space opens the possibility to study more complex systems with many magnetic centers and/or many electrons per center.

cond-mat.str-el↗

arXiv2002

The magnetic structure of Li2CuO2: from ab initio calculations to macroscopic simulations

The magnetic structure of the edge sharing cuprate compound Li2CuO2 has been investigated by means of ab initio electronic structure calculations. The first and second neighbor in-chain magnetic interactions are calculated to be -142 K and 22 K, respectively. The ratio between the two parameters is smaller than suggested previously in the literature. The interchain interactions are antiferromagnetic in nature and of the order of a few Kelvins only. Monte Carlo simulations using the ab initio parameters to define the model Hamiltonian result in a Neel temperature in rather good agreement with experiment. Spin population analysis situate the magnetic moment on the copper and oxygen ions somewhere between the completely localized picture derived from experiment and the more delocalized picture based on local density calculations.

cond-mat.mtrl-sci↗