arXiv subjects

Francesca Menescardi

Publications and source records attributed to Francesca Menescardi.

3 recordsLinked to original sources

arXiv2026

Melting Behavior and Phase Stability of CaO from Neural Network Potentials: a Molecular Dynamics Study

We investigate the melting behavior of calcium oxide (CaO) under extreme conditions, a problem that remains poorly constrained due to experimental limitations despite its relevance for geophysical and technological applications. We develop a Machine Learning Interatomic Potential (MLIP) for CaO with PANNA 2.0 and the LATTE descriptor, training it on a dataset of $\sim$12,000 configurations including solid, liquid, interfacial, and void-containing structures, extracted from ab-initio molecular dynamics data employing PBEsol exchange-correlation functional. We perform large-scale molecular dynamics simulations to compute the melting temperature at ambient pressure using both the void-nucleated melting (VNM) and two-phase coexistence (TPC) methods, obtaining $T_m=3055\pm11$ K and $T_m=2847\pm15$ K, respectively.\\ We calculate an enthalpy of fusion of $\Delta H_f\sim73$ kJ/mol, in agreement with thermodynamic assessments and ab initio calculations. We also reproduce the thermal expansion and obtain a volume increase of $\sim$29% at Tm, consistent with the corresponding decrease in density extracted from spatially resolved number density profiles. Finally, we calculate the high-pressure melting curve of CaO up to 20 GPa, providing one of the very few computational determinations of this quantity to date. The results confirm that the overheating ratio $\eta$ is not constant under pressure, increasing from 17% at ambient pressure to 24% at 20 GPa, confirming previous findings and ruling out the assumption of a fixed overheating ratio. Our results establish MLIP-based simulations as a robust and efficient framework for investigating phase stability in ionic oxides and provide new insight into the melting behavior of CaO under extreme conditions.

cond-mat.mtrl-sci↗

arXiv2024

Melting behavior of CaO at high temperature and pressure: a molecular dynamics study

The thermodynamic behavior of calcium oxide (\ce{CaO}) under high temperature and pressure conditions is critical for understanding the physics of planetary interiors. This study employs molecular dynamics (MD) simulations, including both classical and ab-initio approaches, to investigate the melting behavior of CaO. We calculate the melting temperature of \ce{CaO} by the void-nucleated melting and two-phase coexistence techniques, aiming to resolve discrepancies in experimental data on the melting point, which range from 2843~K to 3223~K in different studies due to the high reactivity and vapor pressure of the substance. The obtained results are $T_f = 3066\pm12$~K and $T_f = 2940\pm65$~K using the void-nucleated melting and the two-phase coexistence method, respectively. Additionally, we calculate the enthalpy of fusion and the high-pressure melting curve, for the first time without making any assumption on the Clapeyron slope. This is extremely important since in experiments the Claperyon slope of the melting curve is estimated from low pressure measurements and the overheating ratio (i.e. $\eta=\frac{T_s}{T_f}-1$, where $T_s$ represents the thermal instability limit corresponding to the homogeneous melting temperature of the solid) is often assumed to be constant in simulations. Our MD results show that $T_s$ increases more rapidly with pressure than $T_f$ and thus that the overheating ratio sensibly depends upon pressure. These findings contribute to the accurate modeling of the CaO phase diagram, which is essential for geochemistry, cosmochemistry, and materials science.

cond-mat.mtrl-sci↗

arXiv2020

High pressure computational search of trivalent lanthanide di-nitrides

Transition metal nitrides have attracted much interest of the scientific community for their intriguing properties and technological applications. Here we focus on yttrium dinitride (YN$_{2}$) and its formation and structural transition under pressure. We employed a fixed composition USPEX search to find the most stable polymorphs. We choose yttrium as a proxy for the lanthanide series because it has only $+3$ oxidation state, contrary to most transition metals. We then computed thermodynamic and dynamical stability of these structures compared to the decomposition reactions and we found that the compound undergoes two structural transitions, the latter showing the formation N$_{4}$ chains. A closer look into the nature of the nitrogen bonding showed that in the first two structures, where nitrogen forms dimers, the bond length is intermediate between that of a single bond and that of a double bond, making it hard to rationalize the proper oxidation state configuration for YN$_{2}$. In the latter structure where there is the formation of N$_{4}$ chains, the bond lengths increase significantly, up to a value that can be justified as a single bond. Finally, we also studied the electronic structure and the dynamical stability of the structures we found.

cond-mat.mtrl-sci↗