arXiv subjects

Cristiano Malica

Publications and source records attributed to Cristiano Malica.

6 recordsLinked to original sources

arXiv2026

Assessing the magnetic states and the accuracy of first-principles Hubbard corrections for the battery cathode Li$_x$CoO$_2$ ($x=0,1$)

Li$_x$CoO$_2$ is a prototypical layered cathode material for Li-ion batteries, yet its accurate description from first principles remains challenging because of self-interaction errors, weak interlayer interactions, and a complex magnetic energy landscape. Here, we present a systematic investigation of the structural, electronic, magnetic, and electrochemical properties of Li$_x$CoO$_2$ ($x=0,1$) using density-functional theory augmented with self-consistent Hubbard corrections and long-range van der Waals interactions, together with a systematic exploration of possible magnetic states. The on-site interactions on Co-$3d$ and O-$2p$ states, as well as inter-site Co-O interactions, are determined from first principles using linear-response theory in the framework of density-functional perturbation theory, with Löwdin-orthogonalized atomic orbitals employed as Hubbard projectors. For LiCoO$_2$, the inclusion of Hubbard corrections provides an accurate description of the structural properties, while the electronic structure is very sensitive to the choice of Hubbard projectors. In particular, frontier Wannier-function projectors substantially improve the description of the occupied electronic states compared with localized atomic orbitals. For CoO$_2$, we demonstrate that a systematic exploration of the magnetic energy landscape is essential to identify the lowest-energy low-spin ground state. However, the resulting Hubbard-corrected electronic structure is insulating, consistent with the prediction of the HSE06 hybrid functional, but in contrast to the experimentally observed metallic behavior. Structural relaxation further drives the system toward a different metallic solution with an electronic configuration inconsistent with low-spin Co$^{4+}$ character. Despite these limitations, the calculated intercalation voltages agree well with experiment, with deviations as small as 2%.

cond-mat.mtrl-sci↗

arXiv2025

First-principles Hubbard parameters with automated and reproducible workflows

We introduce an automated, flexible framework (aiida-hubbard) to self-consistently calculate Hubbard $U$ and $V$ parameters from first-principles. By leveraging density-functional perturbation theory, the computation of the Hubbard parameters is efficiently parallelized using multiple concurrent and inexpensive primitive cell calculations. Furthermore, the intersite $V$ parameters are defined on-the-fly during the iterative procedure to account for atomic relaxations and diverse coordination environments. We demonstrate the scalability and reliability of the framework by computing in high-throughput fashion the self-consistent onsite $U$ and intersite $V$ parameters for 115 Li-containing bulk solids. Our analysis of the Hubbard parameters calculated reveals a significant correlation of the onsite $U$ values on the oxidation state and coordination environment of the atom on which the Hubbard manifold is centered, while intersite $V$ values exhibit a general decay with increasing interatomic distance. We find, e.g., that the numerical values of $U$ for Fe and Mn 3d orbitals can vary up to 3 eV and 6 eV, respectively; their distribution is characterized by typical shifts of about 0.5 eV and 1.0 eV upon change in oxidation state, or local coordination environment. For the intersite $V$ a narrower spread is found, with values ranging between 0.2 eV and 1.6 eV when considering transition metal and oxygen interactions. This framework paves the way for the exploration of redox materials chemistry and high-throughput screening of $d$ and $f$ compounds across diverse research areas, including the discovery and design of novel energy storage materials, as well as other technologically-relevant applications.

cond-mat.mtrl-sci↗

arXiv2024

Teaching oxidation states to neural networks

While the accurate description of redox reactions remains a challenge for first-principles calculations, it has been shown that extended Hubbard functionals (DFT+U+V) can provide a reliable approach, mitigating self-interaction errors, in materials with strongly localized d or f electrons. Here, we first show that DFT+U+V molecular dynamics is capable to follow the adiabatic evolution of oxidation states over time, using representative Li-ion cathode materials. In turn, this allows to develop redox-aware machine-learned potentials. We show that considering atoms with different oxidation states (as accurately predicted by DFT+U+V) as distinct species in the training leads to potentials that are able to identify the correct ground state and pattern of oxidation states for redox elements present. This can be achieved, e.g., through a systematic combinatorial search for the lowest energy configuration or with stochastic methods. This brings the advantages of machine-learned potentials to key technological applications (e.g., rechargeable batteries), which require an accurate description of the evolution of redox states.

cond-mat.mtrl-sci↗

arXiv2021

Quasi-harmonic temperature dependent elastic constants: applications to silicon, aluminum, and silver

We present ab-initio calculations of the quasi-harmonic temperature dependent elastic constants. The isothermal elastic constants are calculated at each temperature as second derivatives of the Helmholtz free energy with respect to strain and corrected for finite pressure effects. This calculation is repeated for a grid of geometries and the results interpolated at the minimum of the Helmholtz free energy. The results are compared with the quasi-static elastic constants. Thermodynamic relationships are used to derive the adiabatic elastic constants that are compared with the experimental measurements. These approaches are implemented for cubic solids in the $\texttt{thermo_pw}$ code and are validated by applications to silicon, aluminum, and silver.

cond-mat.mtrl-sci↗

arXiv2021

Quasi-harmonic thermoelasticity of palladium, platinum, copper, and gold from first principles

We calculate the temperature-dependent elastic constants of palladium, platinum, copper and gold within the quasi-harmonic approximation using a first-principles approach and evaluating numerically the second derivatives of the Helmholtz free-energy with respect to strain at the minimum of the free-energy itself. We find an overall good agreement with the experimental data although the anomalies of palladium and platinum reported at room temperature are not reproduced. The contribution of electronic excitations is also investigated: we find that it is non-negligible for the $C_{44}$ elastic constants of palladium and platinum while it is irrelevant in the other cases. Its effect is not sufficient to explain the details of the anomalies found by experiments, not even when, in the case of platinum, we take into account the electron-phonon interaction. Lastly, the effect of the exchange and correlation functional is addressed and it is found that it is important at T=0 K, while all functionals give similar temperature dependencies.

cond-mat.mtrl-sci↗

arXiv2020

Temperature dependent elastic constants and thermodynamic properties of BAs: an ab-initio investigation

We present an ab-initio study of the temperature dependent elastic constants of BAs, a semiconductor that exhibits ultra-high thermal conductivity and is under investigation for thermal management in electronics. We test the consistency of our predictions by computing the temperature dependent sound velocity of the longitudinal acoustic mode along the $[111]$ direction and comparing with experiment. Furthermore, as a byproduct, we present the room temperature phonon dispersions, and the temperature dependent thermal expansion, isobaric heat capacity, and average Grüneisen parameter comparing with the most updated experiments and previous calculations when available. Finally, we present the theoretical estimate of the temperature dependent mean square atomic displacements.

cond-mat.mtrl-sci↗