In this work, we model and simulate the shape evolution of critically charged droplets, from the ... more In this work, we model and simulate the shape evolution of critically charged droplets, from the initial spherical shape to the charge emission and back to the spherical shape. The shape deformation is described using the viscous correction for viscous potential flow model, which is a potential flow approximation of the Navier-Stokes equation for incompressible Newtonian fluids. The simulated shapes are compared to snapshots of experimentally observed drop deformations. We highlight the influence of the dimensionless viscosity and charge carrier mobility of the liquid on the shape evolution of droplets and discuss the observed trends. We give an explanation as to why the observed deformation pathways of positively and negatively charged pure water droplets differ and give a hint as to why negatively charged water droplets emit more charge during charge breakup than positively charged ones.
We present a theoretical model to study the dynamics of metallic clusters embedded in a rare gas ... more We present a theoretical model to study the dynamics of metallic clusters embedded in a rare gas matrix. We describe the active electrons of the embedded cluster using time dependent density functional theory, while the surrounding matrix is described in terms of classical molecular dynamics of polarizable atoms. The coupling between the cluster and the rare gas atoms is deduced from the work of Groß and Spiegelmann [J. Chem. Phys. 108, 4148 (1998)] and reformulated explicitly in a simple and efficient density functional form. The electron rare gas interaction takes the form of an averaged dipole fluctuation term, which retains the van der Waals long range interaction, and a short range repulsive pseudopotential, which accounts for the Pauli repulsion of the electron by the rare gas atom. We applied our model to Na clusters embedded in Ar matrix. For the latter we developed an efficient local pseudopotential, which allows studying systems containing more than 103 Ar atoms. We show that large systems are indeed necessary to account properly for long range polarization of the matrix, that competes with the matrix confinement effect. We focus our study on Na2, Na4, and Na8. For each system, we have determined the geometry of the most favorable trapping site by means of damped molecular dynamics. We present the effect of matrix embedding on the optical absorption spectrum. For Na2, the trapping site can be unambiguously identified by comparison of the absorption spectrum with experiment. For Na4 the spectrum of the embedded cluster is significantly different from the free cluster spectrum, while for Na8 differences are less pronounced.
We present a non-adiabatic molecular dynamics description of metal clusters subject to violent pe... more We present a non-adiabatic molecular dynamics description of metal clusters subject to violent perturbations. The electronic degrees of freedom are described at a semi-classical level, allowing an account of dynamical correlations, beyond the usual mean ®eld density functional theory (DFT) scheme. Such an extended mean ®eld allows to access highly non-linear dynamics, as generated, for example, through irradiation by intense lasers. We demonstrate on test cases the capability of our approach to describe such situations, as well at the electronic as at the ionic level.
ABSTRACT We present a non-adiabatic molecular dynamics simulation of a Na2+ molecule embedded in ... more ABSTRACT We present a non-adiabatic molecular dynamics simulation of a Na2+ molecule embedded in a single shell solvent made of 17 Ar atoms. The simulation is based on first principles calculation for 1-electron system combined with Tully surface hopping algorithm. The system is promoted to the first excited state and then followed during the first 10ps. The dynamics can be divided into three temporal stages. First, the excess energy is quickly carried out by the Ar atoms aligned with the molecular axis. Second, during the 2 first picosecond, the Na2+ molecule expands and surface hopping takes place. Finally, the system enters a chaotic stage, which determines the issue of the dynamics. Recombination of Na2+ with almost complete evaporation of the solvent atoms occurs for 25% of the trajectories. Dissociation occurs otherwise, leading to the formation of small Na+Arp clusters, with an average value p¯=6.
International audienceThe transmission rate of a low-energy Ar^q+ ion beam through a macroscopic ... more International audienceThe transmission rate of a low-energy Ar^q+ ion beam through a macroscopic glass tube of large aspect ratio is simulated. Secondary electron (SE) emission, induced by ion impacts with the inner surface of the capillary, are taken explicitly into account by adding a SE source term to the charge dynamics equation. We find that the additional SE channel significantly alters the distribution of the deposited charge in the capillary wall. Compared to the case without the SE channel, the electric field generated by the self-organized charge patches is generally weaker, yielding drastically different transmission rates, especially for higher beam intensities. The effect of SEs on the patch formation and resulting transmission rate is found to be significant for SE yields as low as 1 SE per ion impact, in the case of Ar+ ions. We propose a numerical experiment that can be tested experimentally, potentially allowing us to conclude if the SE channel is indeed crucial for accurately simulating the guiding of an ion beam through insulating capillaries. In the long run, our simulations may provide theoretical support for measuring the SE yield of low-energy ions impacting insulating surfaces at grazing angles
International Journal of Modern Physics C, Dec 1, 2001
We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of s... more We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of semi-classical dynamics. We focus on finite fermionic systems such as small metal clusters, which we recently pointed out the importance of the UU collision term for the electronic dynamics. We show, how far the hybrid method, which lies between the full and the parallel ensemble methods, allows an efficient and accurate treatment of a Boltzmann–like collision term. We finally give a guideline to define the best parameter of the hybrid ensemble method for a given cluster size.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Dec 1, 2019
Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a s... more Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a single, insulating macrocapillary is presented. The micrometer sized proton beam was center injected into a poly(tetrafluoroethylene) capillary with macroscopic dimensions. The capillary was tilted to 1°with respect to the beam, i.e. no geometrical transmission was possible, but the beam first hit the inner capillary wall. After a sufficient electric charge-up of the insulator material due to the interaction with the charged particle beam, guiding appeared thanks to the beam deflection caused by the formed electrostatic field. With an increasing amount of the accumulated charge on the wall, the deflection of the beam also increased, resulting in the dynamics of the transmission. When a dynamical equilibrium between the charges being deposited and flowing away in form of leakage current was set in, the deflection of the beam saturated at a certain position. Here, the transmitted fraction of the beam reached 90% relative to the incident beam. At this position the angular distribution of the transmitted beam was determined. In the sample tilting plane focusing effect was observable, while in the perpendicular plane, the beam was defocused.
Experimental data are presented for low-energy singly charged ion transport between two insulatin... more Experimental data are presented for low-energy singly charged ion transport between two insulating parallel plates. Using a beam intensity of approximately 20 pA, measurements of the incoming and transmitted beams provide quantitative temporal information about the charge deposited on the plates and the guiding probability. Using a smaller beam intensity (~ 1 pA) plate charging and discharging properties were studied as a function of time. These data imply that both the charge deposition and decay along the surface and through the bulk need to be modeled as acting independently. A further reduction of beam intensity to ~ 25 fA allowed temporal imaging studies of the positions and intensities of the guided beam plus two bypass beams to be performed. SIMION software was used to simulate trajectories of the guided and bypass beams, to provide information about the amount and location of deposited charge and, as a function of charge patch voltage, the probability of beam guiding and how...
Synopsis The transmission of 1 keV Ar+ ions through a macroscopic glass capillary is simulated by... more Synopsis The transmission of 1 keV Ar+ ions through a macroscopic glass capillary is simulated by taking explicitly into account the secondary electron (SE) emission generated by ion impacts inside the capillary. The SE emission re-distributes the injected charge in the capillary wall and thus modifies the guiding power of insulating capillaries. Especially for high beam intensities, SE are found to be crucial for explaining the observed time-evolution of the transmitted intensities.
In this work, we model and simulate the shape evolution of critically charged droplets, from the ... more In this work, we model and simulate the shape evolution of critically charged droplets, from the initial spherical shape to the charge emission and back to the spherical shape. The shape deformation is described using the viscous correction for viscous potential flow model, which is a potential flow approximation of the Navier-Stokes equation for incompressible Newtonian fluids. The simulated shapes are compared to snapshots of experimentally observed drop deformations. We highlight the influence of the dimensionless viscosity and charge carrier mobility of the liquid on the shape evolution of droplets and discuss the observed trends. We give an explanation as to why the observed deformation pathways of positively and negatively charged pure water droplets differ and give a hint as to why negatively charged water droplets emit more charge during charge breakup than positively charged ones.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019
Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a s... more Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a single, insulating macrocapillary is presented. The micrometer sized proton beam was center injected into a poly(tetrafluoroethylene) capillary with macroscopic dimensions. The capillary was tilted to 1°with respect to the beam, i.e. no geometrical transmission was possible, but the beam first hit the inner capillary wall. After a sufficient electric charge-up of the insulator material due to the interaction with the charged particle beam, guiding appeared thanks to the beam deflection caused by the formed electrostatic field. With an increasing amount of the accumulated charge on the wall, the deflection of the beam also increased, resulting in the dynamics of the transmission. When a dynamical equilibrium between the charges being deposited and flowing away in form of leakage current was set in, the deflection of the beam saturated at a certain position. Here, the transmitted fraction of the beam reached 90% relative to the incident beam. At this position the angular distribution of the transmitted beam was determined. In the sample tilting plane focusing effect was observable, while in the perpendicular plane, the beam was defocused.
We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of s... more We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of semi-classical dynamics. We focus on finite fermionic systems such as small metal clusters, which we recently pointed out the importance of the UU collision term for the electronic dynamics. We show, how far the hybrid method, which lies between the full and the parallel ensemble methods, allows an efficient and accurate treatment of a Boltzmann–like collision term. We finally give a guideline to define the best parameter of the hybrid ensemble method for a given cluster size.
We present a short review on recent theoretical studies of the dynamics of small Na clusters in c... more We present a short review on recent theoretical studies of the dynamics of small Na clusters in contact with Ar matrices, in some cases also on NaCl surfaces. We discuss the hierarchical modeling which treats the cluster fully quantum-mechanically and the substrate at a classical level. The dynamical polarizability of the substrate is properly taken into account. We present results on the structural properties, on dynamics in the regime of linear response, and on fully non-linear dynamics induced by strong femtosecond laser pulses.
The discharge properties of a macroscopic cylindrically shaped glass capillary, initially charged... more The discharge properties of a macroscopic cylindrically shaped glass capillary, initially charged by a 1 keV Ar+ beam tilted by 5° whith respect to the capillary axis is studied. Our experimental observations were compared to our Monte Carlo simulation, higlighting the importance of the surface conductivity.
We present a kinematically complete study of dissociative ionization of D 2 by 13:6 MeV=u S 15 io... more We present a kinematically complete study of dissociative ionization of D 2 by 13:6 MeV=u S 15 ions. The experiment allows us to unravel the competing mechanisms, namely, direct single ionization, autoionization of doubly excited states, ionization excitation, and double ionization, and to analyze the corresponding electron angular distribution from fixed-in-space molecules. The conclusions are supported by theoretical calculations in which the correlated motion of all electrons and nuclei and the interferences between them are described from first principles.
In this work, we model and simulate the shape evolution of critically charged droplets, from the ... more In this work, we model and simulate the shape evolution of critically charged droplets, from the initial spherical shape to the charge emission and back to the spherical shape. The shape deformation is described using the viscous correction for viscous potential flow model, which is a potential flow approximation of the Navier-Stokes equation for incompressible Newtonian fluids. The simulated shapes are compared to snapshots of experimentally observed drop deformations. We highlight the influence of the dimensionless viscosity and charge carrier mobility of the liquid on the shape evolution of droplets and discuss the observed trends. We give an explanation as to why the observed deformation pathways of positively and negatively charged pure water droplets differ and give a hint as to why negatively charged water droplets emit more charge during charge breakup than positively charged ones.
We present a theoretical model to study the dynamics of metallic clusters embedded in a rare gas ... more We present a theoretical model to study the dynamics of metallic clusters embedded in a rare gas matrix. We describe the active electrons of the embedded cluster using time dependent density functional theory, while the surrounding matrix is described in terms of classical molecular dynamics of polarizable atoms. The coupling between the cluster and the rare gas atoms is deduced from the work of Groß and Spiegelmann [J. Chem. Phys. 108, 4148 (1998)] and reformulated explicitly in a simple and efficient density functional form. The electron rare gas interaction takes the form of an averaged dipole fluctuation term, which retains the van der Waals long range interaction, and a short range repulsive pseudopotential, which accounts for the Pauli repulsion of the electron by the rare gas atom. We applied our model to Na clusters embedded in Ar matrix. For the latter we developed an efficient local pseudopotential, which allows studying systems containing more than 103 Ar atoms. We show that large systems are indeed necessary to account properly for long range polarization of the matrix, that competes with the matrix confinement effect. We focus our study on Na2, Na4, and Na8. For each system, we have determined the geometry of the most favorable trapping site by means of damped molecular dynamics. We present the effect of matrix embedding on the optical absorption spectrum. For Na2, the trapping site can be unambiguously identified by comparison of the absorption spectrum with experiment. For Na4 the spectrum of the embedded cluster is significantly different from the free cluster spectrum, while for Na8 differences are less pronounced.
We present a non-adiabatic molecular dynamics description of metal clusters subject to violent pe... more We present a non-adiabatic molecular dynamics description of metal clusters subject to violent perturbations. The electronic degrees of freedom are described at a semi-classical level, allowing an account of dynamical correlations, beyond the usual mean ®eld density functional theory (DFT) scheme. Such an extended mean ®eld allows to access highly non-linear dynamics, as generated, for example, through irradiation by intense lasers. We demonstrate on test cases the capability of our approach to describe such situations, as well at the electronic as at the ionic level.
ABSTRACT We present a non-adiabatic molecular dynamics simulation of a Na2+ molecule embedded in ... more ABSTRACT We present a non-adiabatic molecular dynamics simulation of a Na2+ molecule embedded in a single shell solvent made of 17 Ar atoms. The simulation is based on first principles calculation for 1-electron system combined with Tully surface hopping algorithm. The system is promoted to the first excited state and then followed during the first 10ps. The dynamics can be divided into three temporal stages. First, the excess energy is quickly carried out by the Ar atoms aligned with the molecular axis. Second, during the 2 first picosecond, the Na2+ molecule expands and surface hopping takes place. Finally, the system enters a chaotic stage, which determines the issue of the dynamics. Recombination of Na2+ with almost complete evaporation of the solvent atoms occurs for 25% of the trajectories. Dissociation occurs otherwise, leading to the formation of small Na+Arp clusters, with an average value p¯=6.
International audienceThe transmission rate of a low-energy Ar^q+ ion beam through a macroscopic ... more International audienceThe transmission rate of a low-energy Ar^q+ ion beam through a macroscopic glass tube of large aspect ratio is simulated. Secondary electron (SE) emission, induced by ion impacts with the inner surface of the capillary, are taken explicitly into account by adding a SE source term to the charge dynamics equation. We find that the additional SE channel significantly alters the distribution of the deposited charge in the capillary wall. Compared to the case without the SE channel, the electric field generated by the self-organized charge patches is generally weaker, yielding drastically different transmission rates, especially for higher beam intensities. The effect of SEs on the patch formation and resulting transmission rate is found to be significant for SE yields as low as 1 SE per ion impact, in the case of Ar+ ions. We propose a numerical experiment that can be tested experimentally, potentially allowing us to conclude if the SE channel is indeed crucial for accurately simulating the guiding of an ion beam through insulating capillaries. In the long run, our simulations may provide theoretical support for measuring the SE yield of low-energy ions impacting insulating surfaces at grazing angles
International Journal of Modern Physics C, Dec 1, 2001
We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of s... more We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of semi-classical dynamics. We focus on finite fermionic systems such as small metal clusters, which we recently pointed out the importance of the UU collision term for the electronic dynamics. We show, how far the hybrid method, which lies between the full and the parallel ensemble methods, allows an efficient and accurate treatment of a Boltzmann–like collision term. We finally give a guideline to define the best parameter of the hybrid ensemble method for a given cluster size.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Dec 1, 2019
Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a s... more Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a single, insulating macrocapillary is presented. The micrometer sized proton beam was center injected into a poly(tetrafluoroethylene) capillary with macroscopic dimensions. The capillary was tilted to 1°with respect to the beam, i.e. no geometrical transmission was possible, but the beam first hit the inner capillary wall. After a sufficient electric charge-up of the insulator material due to the interaction with the charged particle beam, guiding appeared thanks to the beam deflection caused by the formed electrostatic field. With an increasing amount of the accumulated charge on the wall, the deflection of the beam also increased, resulting in the dynamics of the transmission. When a dynamical equilibrium between the charges being deposited and flowing away in form of leakage current was set in, the deflection of the beam saturated at a certain position. Here, the transmitted fraction of the beam reached 90% relative to the incident beam. At this position the angular distribution of the transmitted beam was determined. In the sample tilting plane focusing effect was observable, while in the perpendicular plane, the beam was defocused.
Experimental data are presented for low-energy singly charged ion transport between two insulatin... more Experimental data are presented for low-energy singly charged ion transport between two insulating parallel plates. Using a beam intensity of approximately 20 pA, measurements of the incoming and transmitted beams provide quantitative temporal information about the charge deposited on the plates and the guiding probability. Using a smaller beam intensity (~ 1 pA) plate charging and discharging properties were studied as a function of time. These data imply that both the charge deposition and decay along the surface and through the bulk need to be modeled as acting independently. A further reduction of beam intensity to ~ 25 fA allowed temporal imaging studies of the positions and intensities of the guided beam plus two bypass beams to be performed. SIMION software was used to simulate trajectories of the guided and bypass beams, to provide information about the amount and location of deposited charge and, as a function of charge patch voltage, the probability of beam guiding and how...
Synopsis The transmission of 1 keV Ar+ ions through a macroscopic glass capillary is simulated by... more Synopsis The transmission of 1 keV Ar+ ions through a macroscopic glass capillary is simulated by taking explicitly into account the secondary electron (SE) emission generated by ion impacts inside the capillary. The SE emission re-distributes the injected charge in the capillary wall and thus modifies the guiding power of insulating capillaries. Especially for high beam intensities, SE are found to be crucial for explaining the observed time-evolution of the transmitted intensities.
In this work, we model and simulate the shape evolution of critically charged droplets, from the ... more In this work, we model and simulate the shape evolution of critically charged droplets, from the initial spherical shape to the charge emission and back to the spherical shape. The shape deformation is described using the viscous correction for viscous potential flow model, which is a potential flow approximation of the Navier-Stokes equation for incompressible Newtonian fluids. The simulated shapes are compared to snapshots of experimentally observed drop deformations. We highlight the influence of the dimensionless viscosity and charge carrier mobility of the liquid on the shape evolution of droplets and discuss the observed trends. We give an explanation as to why the observed deformation pathways of positively and negatively charged pure water droplets differ and give a hint as to why negatively charged water droplets emit more charge during charge breakup than positively charged ones.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019
Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a s... more Experimental observation of the dynamics of a micro-focused, 1 MeV proton beam guided through a single, insulating macrocapillary is presented. The micrometer sized proton beam was center injected into a poly(tetrafluoroethylene) capillary with macroscopic dimensions. The capillary was tilted to 1°with respect to the beam, i.e. no geometrical transmission was possible, but the beam first hit the inner capillary wall. After a sufficient electric charge-up of the insulator material due to the interaction with the charged particle beam, guiding appeared thanks to the beam deflection caused by the formed electrostatic field. With an increasing amount of the accumulated charge on the wall, the deflection of the beam also increased, resulting in the dynamics of the transmission. When a dynamical equilibrium between the charges being deposited and flowing away in form of leakage current was set in, the deflection of the beam saturated at a certain position. Here, the transmitted fraction of the beam reached 90% relative to the incident beam. At this position the angular distribution of the transmitted beam was determined. In the sample tilting plane focusing effect was observable, while in the perpendicular plane, the beam was defocused.
We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of s... more We present an efficient way to evaluate the Ühling–Uhlenbeck (UU) collision term in the case of semi-classical dynamics. We focus on finite fermionic systems such as small metal clusters, which we recently pointed out the importance of the UU collision term for the electronic dynamics. We show, how far the hybrid method, which lies between the full and the parallel ensemble methods, allows an efficient and accurate treatment of a Boltzmann–like collision term. We finally give a guideline to define the best parameter of the hybrid ensemble method for a given cluster size.
We present a short review on recent theoretical studies of the dynamics of small Na clusters in c... more We present a short review on recent theoretical studies of the dynamics of small Na clusters in contact with Ar matrices, in some cases also on NaCl surfaces. We discuss the hierarchical modeling which treats the cluster fully quantum-mechanically and the substrate at a classical level. The dynamical polarizability of the substrate is properly taken into account. We present results on the structural properties, on dynamics in the regime of linear response, and on fully non-linear dynamics induced by strong femtosecond laser pulses.
The discharge properties of a macroscopic cylindrically shaped glass capillary, initially charged... more The discharge properties of a macroscopic cylindrically shaped glass capillary, initially charged by a 1 keV Ar+ beam tilted by 5° whith respect to the capillary axis is studied. Our experimental observations were compared to our Monte Carlo simulation, higlighting the importance of the surface conductivity.
We present a kinematically complete study of dissociative ionization of D 2 by 13:6 MeV=u S 15 io... more We present a kinematically complete study of dissociative ionization of D 2 by 13:6 MeV=u S 15 ions. The experiment allows us to unravel the competing mechanisms, namely, direct single ionization, autoionization of doubly excited states, ionization excitation, and double ionization, and to analyze the corresponding electron angular distribution from fixed-in-space molecules. The conclusions are supported by theoretical calculations in which the correlated motion of all electrons and nuclei and the interferences between them are described from first principles.
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Papers by eric giglio