arXiv subjects

Pier Luigi Silvestrelli

Publications and source records attributed to Pier Luigi Silvestrelli.

At least 19 recordsLinked to original sources

arXiv2026

Ballistic atomic transport in narrow carbon nanotubes

Friction forces are conventionally modeled via semiclassical theories that associate energy dissipation with newtonian motion on corrugated interface potentials. This consolidated approach is challenged at the nanoscale by observation of nearly unimpeded water flow in narrow carbon nanotubes (CNTs), in spite of nonvanishing energy corrugations. Here we go beyond the standard newtonian perspective, adopting a quantum mechanical description of 4 He flow through narrow CNTs. Building upon our Bloch-wave dynamics [Phys. Rev. Lett. 131, 206301 (2023)] we explore realistic flow conditions, including non-negligible interface interactions, finite temperatures, and imperfect CNTs. At T = 0 K we found that 4 He waves can propagate through ideally periodic, corrugated interface potentials with no friction: below a critical velocity regulated by interface corrugations, energy loss by emission of plasmon and phonon quanta is forbidden. Introducing realistic impurities/defects one still finds very large mean free paths that can exceed the micrometer scale, while thermal phonons and plasmons yield even lower scattering rates. This establishes the unexpected emergence of ballistic wavelike transport in narrow CNTs within realistic nanoscale devices, and demonstrates the intrinsic quantumness of nanoscale interfaces.

cond-mat.mes-hall↗

arXiv2025

Sliding properties of Transition Metal Dichalcogenide bilayers

Transition-metal dichalcogenides (TMDs) are valuable as solid lubricants because of their layered structure, which allows for easy shearing along the basal planes. Using Density Functional Theory (DFT) we conducted a first-principles study of the sliding properties of several TMD bilayers: MoS$_2$, MoTe$_2$, WS$_2$, WSe$_2$, VS$_2$, VSe$_2$, TaS$_2$, TaSe$_2$, TiS$_2$, TiSe$_2$, HfS$_2$, ZrS$_2$, MoS$_2$WS$_2$, MoS$_2$VS$_2$. Given the crucial role of van der Waals (vdW) interactions in accurately describing the interlayer interactions in TMD bilayers, we employed vdW-corrected DFT functionals. Our research confirms the dominance of vdW effects by estimating the fraction of interlayer binding energy attributable to these interactions. We also examined how the choice of different vdW-corrected DFT functionals might influence quantitative results. Using MoS$_2$ as a reference TMD bilayer system, we found that most other TMD bilayers studied exhibit stronger interlayer bonds and greater corrugation. However, TiSe$_2$ shows a profile similar to MoS$_2$, while, interestingly, TiS$_2$, VS$_2$, and ZrS$_2$ are characterized by weaker bonding and lower corrugation than MoS$_2$. We explored relationships between various properties of TMD bilayers, with a particular focus on potential connections between tribological and electronic properties often characteristic of solid interfaces. To this end, we evaluated adhesion energies, work of separation, charge density redistributions in interface regions, differential charge densities, and corrugation. While corrugation and thus resistance to sliding generally tends to increase with the size of the chalcogen element and is typically proportional to the adhesion energy, the relationships between other structural, energetic, and electronic properties do not follow a single, well-defined trend.

cond-mat.mtrl-sci↗

arXiv2024

Screening and antiscreening effects in endohedral nanotubes

Recently we investigated from first principles screening properties in systems where small molecules, characterized by a finite electronic dipole moment, are encapsulated into different nanocages. The most relevant result was the observation of an antiscreening effect in alkali-halide nanocages characterized by ionic bonds. Here we extend the study to another class of nanostructures, the nanotubes. Using first-principles techniques based on the Density Functional Theory, we studied the properties of endohedral nanotubes obtained by encapsulation of a water molecule or a linear HF molecule. A detailed analysis of the effective dipole moment of the complexes and of the electronic charge distribution suggests that screening effects crucially depend not only on the nature of the intramolecular bonds but also on the size and the shape of the nanotubes, and on the specific encapsulated molecule. As observed in endohedral nanocages, screening is maximum in covalent-bond carbon nanotubes, while it is reduced in partially-ionic nanotubes and an antiscreening effect is observed in some ionic nanotubes. However in this case the scenario is more complex than in corresponding ionic nanocages. In fact the specific geometric structure of alkali-halide nanotubes turns out to be crucial for determining the screening/antiscreening behavior: while nanotubes with octagonal transversal section can exhibit an antiscreening effect, which quantitatively depends on the number of layers in the longitudinal direction, instead nanotubes with dodecagonal section are always characterized by a reduction of the total dipole moment, so that a screening behavior is observed. Our results therefore show that, even in nanotube structures, in principle one can tune the dipole moment and generate electrostatic fields at the nanoscale without the aid of external potentials.

physics.chem-ph↗

arXiv2023

Superfluidity meets the solid-state: frictionless mass-transport through a (5,5) carbon-nanotube

Superfluidity is a well-characterized quantum phenomenon which entails frictionless-motion of mesoscopic particles through a superfluid, such as $^4$He or dilute atomic-gases at very low temperatures. As shown by Landau, the incompatibility between energy- and momentum-conservation, which ultimately stems from the spectrum of the elementary excitations of the superfluid, forbids quantum-scattering between the superfluid and the moving mesoscopic particle, below a critical speed-threshold. Here we predict that frictionless-motion can also occur in the absence of a standard superfluid, i.e. when a He atom travels through a narrow (5,5) carbon-nanotube (CNT). Due to the quasi-linear dispersion of the plasmon and phonon modes that could interact with He, the (5,5) CNT embodies a solid-state analog of the superfluid, thereby enabling straightforward transfer of Landau's criterion of superfluidity. As a result, Landau's equations acquire broader generality, and may be applicable to other nanoscale friction phenomena, whose description has been so far purely classical.

cond-mat.mtrl-sci↗

arXiv2023

Transport properties in liquids from first principles: the case of liquid water and liquid Argon

Shear and bulk viscosity of liquid water and Argon are evaluated from first principles in the Density Functional Theory (DFT) framework, by performing Molecular Dynamics simulations in the NVE ensemble and using the Kubo-Greenwood equilibrium approach. Standard DFT functional is corrected in such a way to allow for a reasonable description of van der Waals (vdW) effects. For liquid Argon the thermal conductivity has been also calculated. Concerning liquid water, to our knowledge this is the first estimate of the bulk viscosity and of the shear-viscosity/bulk-viscosity ratio from first principles. By analyzing our results we can conclude that our first-principles simulations, performed at a nominal average temperature of 366 K to guarantee that the systems is liquid-like, actually describe the basic dynamical properties of liquid water at about 330 K. In comparison with liquid water, the normal, monatomic liquid Ar is characterized by a much smaller bulk-viscosity/shear-viscosity ratio (close to unity) and this feature is well reproduced by our first-principles approach which predicts a value of the ratio in better agreement with experimental reference data than that obtained using the empirical Lennard-Jones potential. The computed thermal conductivity of liquid Argon is also in good agreement with the experimental value.

cond-mat.soft↗

arXiv2022

Quantum-mechanically enhanced water flow in sub-nanometer carbon nanotubes

Water-flow in carbon nanotubes (CNT's) starkly contradicts classical fluid mechanics, with permeabilities that can exceed no-slip Haagen-Poiseuille predictions by two to five orders of magnitude. Semi-classical molecular dynamics accounts for enhanced flow-rates, that are attributed to curvature-dependent lattice mismatch. However, the steeper permeability-enhancement observed experimentally at $\sim$nm-size radii remains poorly understood, and suggests emergence of puzzling non-classical mechanisms. Here we address water-CNT friction from a quantum-mechanical perspective, in terms of water-energy loss upon phonon excitation. We find that combined weak water-phonon coupling and selection rules hinder water-CNT scattering, providing effective protection to water superflow, whereas comparison with a semiclassical theory evidences a friction increase that can exceed the quantum-mechanical prediction by more than two orders of magnitude. Quasi-frictionless flow up to sub-nm CNT's opens new pathways towards minimally-invasive trans-membrane cellular injections, single-water fluidics and efficient water filtration.

cond-mat.mtrl-sci↗

arXiv2021

Localization versus inhomogeneous superfluidity: Submonolayer He-4 on fluorographene, hexagonal boron nitride, and graphene

We study a sub monolayer He-4 adsorbed on fluorographene (GF) and on hexagonal boron nitride (hBN) at low coverage. The adsorption potentials have been computed ab-initio with a suitable density functional theory including dispersion forces. The properties of the adsorbed He-4 atoms have been computed at finite temperature with path integral Monte Carlo and at T=0 K with variational path integral. From both methods we find that the lowest energy state of He-4 on GF is a superfluid. Due to the very large corrugation of the adsorption potential this superfluid has a very strong spatial anisotropy, the ratio between the largest and smallest areal density being about 6, the superfluid fraction at the lowest T is about 55%, and the temperature of the transition to the normal state is in the range 0.5-1 K. Thus, GF offers a platform for studying the properties of a strongly interacting highly anisotropic bosonic superfluid. At a larger coverage He-4 has a transition to an ordered commensurate state with occupation of 1/6 of the adsorption sites. This phase is stable up to a transition temperature located between 0.5 and 1~K. The system has a triangular order similar to that of He-4 on graphite. The lowest energy state of He-4 on hBN is an ordered commensurate state with occupation of 1/3 of the adsorption sites and triangular symmetry. A disordered state is present at lower coverage as a metastable state. In the presence of an electric field the corrugation of the adsorption potential is slightly increased but up to a magnitude of 1 V/Ang. the effect is small and does not change the stability of the phases of He-4 on GF and hBN. We have verified that also in the case of graphene such electric field does not modify the stability of the commensurate sqrt{3}*sqrt{3}R30 phase.

cond-mat.other↗

arXiv2019

Prediction for two spatially modulated superfluids: $^4$He on fluorographene and on hexagonal BN

We have derived the adsorption potential of $^4$He atoms on fluorographene (GF), on graphane and on hexagonal boron nitride (hBN) by a recently developed ab initio method that incorporates the van der Waals interaction. The $^4$He monolayer on GF and on hBN is studied by state-of-the-art quantum simulations at T=0 K. With our adsorption potentials we find that in both cases the ground state of $^4$He monolayer is a fluid and not an ordered state with localized atoms as on graphite and on graphene. In the case of GF the present result is in qualitative agreement with the superfluid phase that was obtained using an empirical adsorption potential [M. Nava et al., Phys. Rev. B 86, 174509 (2012)]. This fluid state of $^4$He on GF and on hBN is characterized by a very large density modulation and at the equilibrium density the ratio $Γ$ between the largest and the smallest local density along the direction of two neighboring adsorption sites and averaged over the perpendicular direction is $Γ$ = 1.91 for GF and $Γ$ = 1.65 for hBN. Recent experiments [J. Nyeki et al., Nature Physics 13, 455 (2017)] have discovered a superfluid phase in the second layer $^4$He. This is a spatially modulated superfluid that turns out to have anomalous thermal properties. This gives a strong motivation for an experimental study of monolayer $^4$He on GF and on hBN that we predict to be a superfluid with a much stronger spatial modulation.

cond-mat.mes-hall↗

arXiv2019

Van der Waals Interactions in DFT using Wannier Functions without empirical parameters

A new implementation is proposed for including van der Waals (vdW) interactions in Density Functional Theory (DFT) using the Maximally-Localized Wannier functions (MLWFs), which is free from empirical parameters. With respect to the previous DFT/vdW-WF2 method, in the present DFT/vdW-WF2-x approach, the empirical, short-range, damping function is replaced by an estimate of the Pauli exchange repulsion, also obtained by the MLWFs properties. Applications to systems contained in the popular S22 molecular database and to the case of an Ar atom interacting with graphite, and comparison with reference data, indicate that the new method, besides being more physically founded, also leads to a systematic improvement in the description of vdW-bonded systems.

physics.chem-ph↗

arXiv2018

Hidden by graphene -- towards effective screening of interface van der Waals interactions via monolayer coating

Recent atomic force microscopy (AFM) experiments~[ACS Nano {\bf 2014}, 8, 12410-12417] conducted on graphene-coated SiO$_2$ demonstrated that monolayer graphene (G) can effectively screen dispersion van der Waals (vdW) interactions deriving from the underlying substrate: despite the single-atom thickness of G, the AFM tip was almost insensitive to SiO$_2$, and the tip-substrate attraction was essentially determined only by G. This G vdW {\it opacity} has far reaching implications, encompassing stabilization of multilayer heterostructures, micromechanical phenomena or even heterogeneous catalysis. Yet, detailed experimental control and high-end applications of this phenomenon await sound physical understanding of the underlying physical mechanism. By quantum many-body analysis and ab-initio Density Functional Theory, here we address this challenge providing theoretical rationalization of the observed G vdW {\it opacity} for weakly interacting substrates. The non-local density response and ultra slow decay of the G vdW interaction ensure compensation between standard attractive terms and many-body repulsive contributions, enabling vdW {\it opacity} over a broad range of adsorption distances. vdW {\it opacity} appears most efficient in the low frequency limit and extends beyond London dispersion including electrostatic Debye forces. By virtue of combined theoretical/experimental validation, G hence emerges as a promising ultrathin {\it shield} for modulation and switching of vdW interactions at interfaces and complex nanoscale devices.

cond-mat.mtrl-sci↗

arXiv2017

Physical Adsorption at the Nanoscale: Towards Controllable Scaling of the Substrate-Adsorbate van der Waals Interaction

The Lifshitz-Zaremba-Kohn (LZK) theory is commonly considered as the correct large-distance limit for the van der Waals (vdW) interaction of adsorbates (atoms, molecules, or nanoparticles) with solid substrates. In the standard approximate form, implicitly based on "local" dielectric functions, the LZK approach predicts universal power laws for vdW interactions depending only on the dimensionality of the interacting objects. However, recent experimental findings are challenging the universality of this theoretical approach at finite distances of relevance for nanoscale assembly. Here, we present a combined analytical and numerical many-body study demonstrating that physical adsorption can be significantly enhanced at the nanoscale. Regardless of the band gap or the nature of the adsorbate specie, we find deviations from conventional LZK power laws that extend to separation distances of up to 10--20 nanometers. Comparison with recent experimental observation of ultra long-ranged vdW interactions in the delamination of graphene from a silicon substrate reveals qualitative agreement with the present theory. The sensitivity of vdW interactions to the substrate response and to the adsorbate characteristic excitation frequency also suggests that adsorption strength can be effectively tuned in experiments, paving the way to an improved control of physical adsorption at the nanoscale.

cond-mat.mtrl-sci↗

arXiv2017

Hydrogen bonding characterization in water and small molecules

The prototypical Hydrogen bond in water dimer and Hydrogen bonds in the protonated water dimer, in other small molecules, in water cyclic clusters, and in ice, covering a wide range of bond strengths, are theoretically investigated by first-principles calculations based on the Density Functional Theory, considering a standard Generalized Gradient Approximation functional but also, for the water dimer, hybrid and van-der-Waals corrected functionals. We compute structural, energetic, and electrostatic (induced molecular dipole moments) properties. In particular, Hydrogen bonds are characterized in terms of differential electron densities distributions and profiles, and of the shifts of the centres of Maximally localized Wannier Functions. The information from the latter quantities can be conveyed into a single geometric bonding parameter that appears to be correlated to the Mayer bond order parameter and can be taken as an estimate of the covalent contribution to the Hydrogen bond. By considering the cyclic water hexamer and the hexagonal phase of ice we also elucidate the importance of cooperative/anticooperative effects in Hydrogen-bonding formation.

physics.chem-ph↗

arXiv2016

Dynamical spin properties of confined Fermi and Bose systems in presence of spin-orbit coupling

Due to the recent experimental progress, tunable spin-orbit (SO) interactions represent ideal candidates for the control of polarization and dynamical spin properties in both quantum wells and cold atomic systems. A detailed understanding of spin properties in SO coupled systems is thus a compelling prerequisite for possible novel applications or improvements in the context of spintronics and quantum computers. Here we analyze the case of equal Rashba and Dresselhaus couplings in both homogeneous and laterally confined two-dimensional systems. Starting from the single-particle picture and subsequently introducing two-body interactions we observe that periodic spin fluctuations can be induced and maintained in the system. Through an analytical derivation we show that the two-body interaction does not involve decoherence effects in the bosonic dimer, and, in the repulsive homogeneous Fermi gas it may be even exploited in combination with the SO coupling to induce and tune standing currents. By further studying the effects of a harmonic lateral confinement --a particularly interesting case for Bose condensates-- we evidence the possible appearance of non-trivial {\it spin textures}, whereas the further application of a small Zeeman-type interaction can be exploited to fine-tune the system polarizability.

cond-mat.quant-gas↗

arXiv2016

van der Waals-corrected Density Functional Theory simulation of adsorption processes on noble-metal surfaces: Xe on Ag(111), Au(111), and Cu(111)

The DFT/vdW-WF2s1 method based on the generation of localized Wannier functions, recently developed to include the van der Waals interactions in the Density Functional Theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe with noble-metal surfaces, namely Ag(111), Au(111), and Cu(111). The study is also repeated by adopting the DFT/vdW-QHO-WF variant relying on the Quantum Harmonic Oscillator model which describes well many-body effects. Comparison of the computed equilibrium binding energies and distances, and the $C_3$ coefficients characterizing the adatom-surface van der Waals interactions, with available experimental and theoretical reference data shows that the methods perform well and elucidate the importance of properly including screening effects. The results are also compared with those obtained by other vdW-corrected DFT schemes, including PBE-D, vdW-DF, vdW-DF2, rVV10, and by the simpler Local Density Approximation (LDA) and semilocal (PBE) Generalized Gradient Approximation (GGA) approaches.

physics.chem-ph↗

arXiv2016

Cohesive properties of noble metals by van der Waals-corrected Density Functional Theory

The cohesive energy, equilibrium lattice constant, and bulk modulus of noble metals are computed by different van der Waals-corrected Density Functional Theory methods, including vdW-DF, vdW-DF2, vdW-DF-cx, rVV10 and PBE-D. Two specifically-designed methods are also developed in order to effectively include dynamical screening effects: the DFT/vdW-WF2p method, based on the generation of Maximally Localized Wannier Functions, and the RPAp scheme (in two variants), based on a single-oscillator model of the localized electron response. Comparison with results obtained without explicit inclusion of van der Waals effects, such as with the LDA, PBE, PBEsol, or the hybrid PBE0 functional, elucidates the importance of a suitable description of screened van der Waals interactions even in the case of strong metal bonding. Many-body effects are also quantitatively evaluated within the RPAp approach.

physics.chem-ph↗

arXiv2015

van der Waals-corrected Density Functional Theory simulation of adsorption processes on transition-metal surfaces: Xe and graphene on Ni(111)

The DFT/vdW-WF2s1 method, recently developed to include the van der Waals interactions in the Density Functional Theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe and graphene with a transition-metal surface, namely Ni(111). In general the adsorption of rare-gas atoms on metal surfaces is important because is prototypical for physisorption processes. Moreover, the interaction of graphene with Ni(111) is of particular interest for practical applications (efficient and large-scale production of high-quality graphene) and, from a theoretical point of view, is particularly challenging, since it can be described by a delicate interplay between chemisorption and physisorption processes. The first-principles simulation of transition metals require particular care also because they can be viewed as intermediate systems between simple metals and insulating crystals. Even in these cases the method performs well as demonstrated by comparing our results with available experimental data and other theoretical investigations. We confirm that the rare gas Xe atom is preferentially adsorbed on the top-site configuration on the Ni(111) surface too. Our approach based on the use of the Maximally Localized Wannier Functions also allow us to well characterize the bonds between graphene and Ni(111).

cond-mat.mtrl-sci↗

arXiv2014

Polarization of a quasi two-dimensional repulsive Fermi gas with Rashba spin-orbit coupling: a variational study

Motivated by the remarkable experimental control of synthetic gauge fields in ultracold atomic systems, we investigate the effect of an artificial Rashba spin-orbit coupling on the spin polarization of a two-dimensional repulsive Fermi gas. By using a variational many-body wavefunction, based on a suitable spinorial structure, we find that the polarization properties of the system are indeed controlled by the interplay between spin-orbit coupling and repulsive interaction. In particular, two main effects are found: 1) The Rashba coupling determines a gradual increase of the degree of polarization beyond the critical repulsive interaction strength, at variance with conventional 2D Stoner instability. 2) The critical interaction strength, above which finite polarization is developed, shows a dependence on the Rashba coupling, i.e. it is enhanced in case the Rashba coupling exceeds a critical value. A simple analytic expression for the critical interaction strength is further derived in the context of our variational formulation, which allows for a straightforward and insightful analysis of the present problem.

cond-mat.quant-gas↗

arXiv2014

Including screening in van-der-Waals corrected DFT calculations. The case of atoms and small molecules physisorbed on graphene

The DFT/vdW-QHO-WF method, recently developed to include the van der Waals (vdW) interactions in approximated Density Functional Theory (DFT) by combining the Quantum Harmonic Oscillator model with the Maximally Localized Wannier Function technique, is applied to the cases of atoms and small molecules (X=Ar, CO, H$_2$, H$_2$O) weakly interacting with benzene and with the ideal planar graphene surface. Comparison is also presented with the results obtained by other DFT vdW-corrected schemes, including PBE+D, vdW-DF, vdW-DF2, rVV10, and by the simpler Local Density Approximation (LDA) and semilocal Generalized Gradient Approximation (GGA) approaches. While for the X-benzene systems all the considered vdW-corrected schemes perform reasonably well, it turns out that an accurate description of the X-graphene interaction requires a proper treatment of many-body contributions and of short-range screening effects, as demonstrated by adopting an improved version of the DFT/vdW-QHO-WF method. We also comment on the widespread attitude of relying on LDA to get a rough description of weakly interacting systems.

cond-mat.mtrl-sci↗