arXiv subjects

Clotilde S. Cucinotta

Publications and source records attributed to Clotilde S. Cucinotta.

10 recordsLinked to original sources

arXiv2026

Disentangling Surface Charge and Electrolyte Effects on Interfacial Water at Electrified Pt(111)

The structure of interfacial water at electrified metal electrodes is known to affect electrocatalysis, and experiments highlight its sensitivity to electrolyte ion identity and applied bias. To disentangle generic charge-controlled structural changes from ion-specific effects, we compare ab initio molecular dynamics water structures at electrified Pt(111) generated with two very different biasing schemes: an explicit ion imbalance in the double layer and homogeneously distributed partially charged hydrogen atoms. Despite these distinct counter-charge representations, both approaches yield a consistent average response of the first water bilayer, in particular of the chemisorbed first layer, when compared on a common surface-charge scale. Method-dependent differences, in particular those associated with explicit electrolyte ions, become apparent only in more local structural descriptors. The hydrogen-bond topology reveals charge-dependent chain-to-ring rearrangements, with explicit ions enhancing ring populations near the potential of zero charge. Layer-resolved vibrational density of states (VDOS) assigns the strongest O-H stretching perturbation to chemisorbed first-layer water and identifies high-frequency signatures of ion-coordinated water, while computed vibrational sum-frequency generation (VSFG) spectra show that the physisorbed, electrolyte-facing region is particularly sensitive to the counter-charge representation. These results suggest that surface charge controls the average structural response, whereas electrolyte ions and their solvation shells become visible only when locally refined descriptors are investigated or probed, e.g. the H-bond network topology and vibrational fingerprints of the interfacial bilayer.

cond-mat.mtrl-sci↗

arXiv2026

Electrostatic Phenomenology Benchmarks for Machine-Learned Interatomic Potentials in Electrochemistry: Beyond the Energy-Force Metric

Accurate treatment of long-range interactions in machine learning interatomic potentials (MLIPs) is essential for electrochemical simulations. However, aggregate energy and force errors alone are insufficient to establish an MLIP's physical accuracy since they do not detect qualitative inconsistencies in the model such as the prediction of image-charge attraction, dielectric screening, or charge transfer. We introduce a benchmark suite EPhEct (Electrostatic Phenomena for Electrochemistry) of focused test cases designed to evaluate MLIPs on electrochemically relevant physical phenomena. The tests probe for image-charge attraction at a metal electrode, the splitting between longitudinal and transverse optical phonons as a probe of ionic and electronic screening, the dipole moment of interfacial water, and Fermi-level pinning during ion discharge. These tests establish a qualitative diagnostic routine complementary to aggregate energy-force metrics.

cond-mat.mtrl-sci↗

arXiv2026

CP2K: An electronic structure and molecular dynamics software package - Dynamics, Transport, and Spectroscopic Response

One of the distinguishing aspects of CP2K is its seamless integration of diverse structural and transition-state optimization techniques with advanced sampling approaches including Monte Carlo, molecular dynamics, and metadynamics, enabling the efficient exploration of complex potential- and free-energy landscapes, including rare events. These capabilities are combined with a broad hierarchy of energy and force evaluation methods, ranging from classical and machine-learned interaction potentials and mixed quantum-classical multiscale and semiempirical schemes, to highly accurate quantum-mechanical electronic-structure approaches. At the heart of the latter lies the Gaussian and plane-wave framework, along with its augmented all-electron generalization, which have been described in detail in our previous code review [T. D. Kühne et al., J. Chem. Phys. 152, 194103 (2020)]. Building on this foundation, the present work revisits the methods within CP2K that turn electronic structure into dynamics, transport, and spectroscopic response. Particular emphasis is placed on the coupling between static response calculations and nuclear motion: spectra may be evaluated at optimized structures, averaged over thermally sampled configurations, obtained from time-correlation functions along ab-initio or path integral molecular trajectories, or followed in real time together with electronic and nuclear dynamics. The same modular structure also enables equilibrium and biased transport simulations, from Kubo-type linear response to open-boundary approaches under external potentials, highlighting CP2K's unique capability to unify quantum chemistry with quantum and statistical mechanics within a versatile, holistic simulation environment.

physics.chem-ph↗

arXiv2026

Divergent Fluctuations from a 2D Infrared Catastrophe

Molecular simulations of interfacial polar media routinely employ periodic boundary conditions parallel to the interface. We show that this lateral periodicity introduces a spatially uniform in-plane mode ($q_{\parallel}=0$) that is unscreened because every lateral replica carries identical charge fluctuations. This 2D mode reduces the plane-averaged potential to a stochastic integral of the plane-averaged charge density along $z$, so that in a semi-infinite slab the variance of the potential grows linearly with depth. In a finite or periodic cell along $z$, with boundaries held at fixed potential, it follows a parabolic profile--a Brownian bridge--pinned to zero at both ends, with amplitude inversely proportional to the lateral cell area. These diverging fluctuations are a pure artifact of the imposed 2D lateral periodicity: they remain bounded in systems that are non-periodic or of finite lateral extent. We provide an analytic expression for their magnitude in dipolar media, yielding a practical criterion for the choice of lateral cell dimensions.

cond-mat.stat-mech↗

arXiv2025

Nanoscale surface morphology controls charge storage at stepped Pt-water interfaces

Platinum step edges dominate electrocatalytic activity in fuel cells and electrolysers, yet their atomistic electrochemical behaviour remains poorly understood. Here, we employ \textit{ab initio} molecular dynamics under controlled electrode potentials to model a realistic stepped Pt--water interface incorporating experimentally observed (111)$\times$(111) and (111)$\times$(100) edge motifs. This allows us to resolve, for the first time, the site-specific structure, charge distribution, and electrostatics of the electric double layer at a nanostructured Pt surface. We find that differential capacitance near the potential of zero charge (PZC) arises almost entirely from potential-dependent chemisorption of water on flat (111) terraces. In contrast, step edges are saturated with chemisorbed water even below the PZC and thus do not contribute to the capacitance. Instead, edges accumulate excess positive charge and exhibit a locally elevated electrostatic potential, as revealed by spatially resolved macroscopic potential profiles. This electrostatic asymmetry implies a greater barrier for electron accumulation at step sites compared to terraces, consistent with enhanced charge localisation and reactivity. Finally, the higher-in-energy d-band centre and sharper projected density of states at edge atoms further support their role as active, positively charged centres. Together, these results provide a mechanistic explanation for the observed experimental shift of the PZC with step density and establish a predictive framework for understanding and optimising interfacial charging in nanostructured Pt electrocatalysts.

cond-mat.mtrl-sci↗

arXiv2024

Enabling Ab-Initio Molecular Dynamics under Bias: The CP2K+SMEAGOL Interface for Integrating Density Functional Theory and Non-Equilibrium Green Functions

Density functional theory (DFT) combined with non-equilibrium Greens functions (NEGF) is a powerful approach to model quantum transport under external bias potentials, at reasonable computational cost. In this work we present a new interface between the popular mixed Gaussian/plane wave electronic structure package CP2K and the NEGF code SMEAGOL, the most feature-rich implementation of DFT-NEGF available for CP2K to-date. The CP2K+SMEAGOL interface includes the implementation of current induced forces. We verify this implementation for a variety of systems: an infinite 1D Au wire, a parallel-plate capacitor and a Au-H2-Au junction. We find good agreement with SMEAGOL calculations performed with SIESTA for the same systems, and with the example of a solvated Au wire demonstrate for the first time that DFT-NEGF can be used to perform molecular dynamics simulations under bias of large-scale condensed phase systems under realistic operating conditions.

cond-mat.mtrl-sci↗

arXiv2023

Revealing Local Field Effects at the Electrical Double Layer with Efficient Open Boundary Simulations under Potential Control

A major challenge in modelling interfacial processes in electrochemical (EC) devices is performing simulations at constant potential. This requires an open-boundary description of the electrons, so that they can enter and leave the computational cell. To enable realistic modelling of EC processes under potential control we have interfaced Density Functional Theory with the Hairy Probe method in the weak coupling limit (DOI: 10.1103/PhysRevB.97.045116). Our implementation was systematically tested using simple parallel-plate capacitor models with pristine surfaces and a single layer of adsorbed water molecules. Remarkably, our code's efficiency is comparable with a standard DFT calculation. We reveal that local field effects at the electrical double layer induced by the change of applied potential can significantly affect the energies of chemical steps in heterogeneous electrocatalysis. Our results demonstrate the importance of an explicit modelling of the applied potential in a simulation and provide an efficient tool to control this critical parameter.

physics.chem-ph↗

arXiv2019

The nanoscale structure of the Pt-water double layer under bias revealed

The nanoscopic mass and charge distribution within the double layer at electrified interfaces plays a key role in electrochemical phenomena of huge technological relevance for energy production and conversion. However, in spite of its importance, the nanoscopic structure of the double layer and its response to an applied potential is still almost entirely unknown, even for Pt-water, the most fundamental electrochemical interface. Using a general ab initio methodology which advances previous models towards a dynamic and more realistic description of an electrode/electrolyte interface, we simulate for the first time the nanoscopic structure of the Pt-water double layer and its response to an applied potential, in realistic solution conditions. We reveal that the nanoscopic metal/surface structure and charging are not captured by traditional capacitor models, as the electrode polarization is associated with a charge oscillation within the double layer and a densification of the water layer in contact with the electrode, both of which strongly depend on the applied potential. Furthermore, we demonstrate that the interface dipole is not determined by the reorientation of the first water layer in contact with the electrode, but by its charging state in combination with its number density, while water reorientation becomes relevant only in the second water layer. Our findings will be essential to develop highly realistic models for the catalytic processes at the Pt-water interface.

physics.chem-ph↗

arXiv2015

An in- and ex-situ TEM study into the oxidisation of titanium (IV) sulphide

The degradation of liquid dispersed titanium (IV) sulphide (TiS$_2$) is studied from the point of view of oxidisation. TiS$_2$ is a layered two-dimensional nanomaterial, with potential for energy storage applications. However, flakes in dispersion were observed to degrade. We examined two oxidisation routes: deionised water at room temperature and oxygen gas within the temperature range 150-350°C. Water was seen to slowly oxidise flakes inwards from the edge, forming an amorphous oxide, a result comparable to the state of flakes which degraded within the original dispersion. Oxygen gas was seen to rapidly oxidise entire flakes to a polycrystalline oxide, when heated 275 °C and above. Degradation was studied with scanning transmission electron microscopy (STEM), energy dispersed x-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS). Density Functional Theory calculations have shown oxidisation by both water and gas molecules to be thermodynamically favourable.

cond-mat.mtrl-sci↗

arXiv2015

Liquid exfoliation of solvent-stabilised black phosphorus: applications beyond electronics

Few layer black phosphorus is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of stability severely limits our ability to synthesise and process this material. Here we demonstrate that high-quality, few-layer black phosphorus nanosheets can be produced in large quantities by liquid phase exfoliation in the solvent N-cyclohexyl-2-pyrrolidone (CHP). We can control nanosheet dimensions and have developed metrics to estimate both nanosheet size and thickness spectroscopically. When exfoliated in CHP, the nanosheets are remarkably stable unless water is intentionally introduced. Computational studies show the degradation to occur by reaction with water molecules only at the nanosheet edge, leading to the removal of phosphorus atoms and the formation of phosphine and phosphorous acid. We demonstrate that liquid exfoliated black phosphorus nanosheets are potentially useful in a range of applications from optical switches to gas sensors to fillers for composite reinforcement.

cond-mat.mes-hall↗