Pietro Cortona | Ecole Centrale Paris (original) (raw)
Papers by Pietro Cortona
Http Www Theses Fr, 2003
Les trois surfaces de plus bas indices de Miller du Cuivre ainsi que la reconstruction de la surf... more Les trois surfaces de plus bas indices de Miller du Cuivre ainsi que la reconstruction de la surface (110) suite a l'adsorption d'oxygene atomique ont ete etudiees dans cette these. Il a fallu pour cela developper les outils necessaires d'une part a la modelisation de la structure des bandes d'energie de ces surfaces et d'autre part a l'ajustement des bandes calculees sur des donnees experimentales obtenues par photo-emission directe et inverse. Cela a ete realise en combinant la methode LCAO empirique d'interpolation de calculs de bandes d'e��nergie des solides et un programme de minimisation de fonctions a plusieurs parametres. Dans la premiere etape, qui a consiste a modeliser un cristal massif ainsi que les principales surfaces propres, nous avons inclus dans le processus d'ajustement des donnees experimentales issues de mesures sur la surface (110), ce qui nous a permis d'obtenir un seul ensemble de parametres decrivant les interactions des atomes dans le Cuivre massif et applicable aux etudes des surfaces. Cet ensemble de parametres a donne une structure de bandes du volume et des surfaces en accord tres pousse avec les donnees experimentales, ce qui n'existait pas jusqu'a present dans la litterature. Nous avons ensuite etabli un deuxieme ensemble de parametres afin de prendre en compte les interactions d'atomes d'oxygene avec un substrat de Cuivre, ce dernier etant decrit par les parametres precedemment obtenus. Nous avons ainsi pu modeliser la structure des bandes de la surface (110) oxydee dans ses plus fins details, et notamment la dispersion et la symetrie des etats anti-liants de l'oxygene, ce qui n'avait jamais ete realise auparavant ni dans le cadre d'une modelisation LCAO, ni dans le cadre de calculs ab-initio. Les applications de ces calculs sont multiples, et tous les travaux menes pour etudier le cristal de Cuivre et ses principales surfaces peuvent etre reconduits pour d'autres metaux de transition.
Journal of Electronic Materials, 2012
Density functional theory and the Boltzmann transport equation were used to calculate the thermoe... more Density functional theory and the Boltzmann transport equation were used to calculate the thermoelectric transport coefficients for bulk V 2 O 5 and MV 2 O 5 (M = Cr, Ti, Na, Li). The structural relaxation for the given compounds based on the ABINIT code was observed. The temperature dependences of the Seebeck coefficients as well as electrical and thermal electrical conductivities of all relaxed structures displayed anisotropic behavior. Electrooptical measurements of thermoelectric properties were carried out on V 2 O 5 thin films obtained by thermal evaporation with different post-annealing treatments. A Seebeck coefficient of À148 lV/K at T = 300 K was obtained in the in-plane direction for V 2 O 5 thin films with thickness less than 100 nm.
Physical Review A, 2019
A theoretical approach for the electron-impact vibronic excitation of molecular ions with low-lyi... more A theoretical approach for the electron-impact vibronic excitation of molecular ions with low-lying excited electronic states is described. In this approach, the fixed-nuclear R-matrix method is employed to compute electron-ion scattering matrices in the Born-Oppenheimer approximation. A vibronic frame transformation and the closed-channel elimination procedure in a spirit of molecular quantum defect theory are employed to construct an energy-dependent scattering matrix describing interactions between vibronic channels of the target ion induced by the incident electron. The obtained scattering matrix accounts for Rydberg series of vibronic resonances in the collisional spectrum. The approach is applied to the CH + ion of an astrophysical and technological interest. Cross sections for vibronic excitation for different combinations of initial and final vibronic states are computed. A good agreement between electronic-excitation cross sections, obtained using the quantum defect theory and in a direct R-matrix calculation, demonstrates that the present approach provides a reliable tool for determination of vibronic (de-)excitation cross sections for targets with low-energy electronic resonances. Such targets were difficult to treat theoretically using earlier methods.
Plasma Sources Science and Technology, 2019
In this study, we compute cross sections for vibrational excitation of NO2 by electron impact. Ca... more In this study, we compute cross sections for vibrational excitation of NO2 by electron impact. Calculations are performed using a theoretical approach based on a combination of the normal mode approximation for vibrational states of the target molecule, fixed-nuclei electron-NO2 scattering matrices and the vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions. Thermally-averaged rate coefficients are derived from the obtained cross sections for temperatures in the 10–10000 K interval for excitation of each normal mode of the target molecule. Analytical fits for the rate coefficients for singlets and triplets are provided. In addition, a comprehensive set of calculations are performed for assessing the uncertainty of the present calculations. The uncertainty assessments indicate that the computed observables for vibrational (de-)excitation is reasonable for later use in NO2-containing plasma kinetics modeling.
Physical Review B, 2016
Using the semiclassical neutral atom theory, we extend to fourth order the modified gradient expa... more Using the semiclassical neutral atom theory, we extend to fourth order the modified gradient expansion of the exchange energy of density functional theory. This expansion can be applied both to large atoms and solid-state problems. Moreover, we show that it can be employed to construct a simple and non-empirical generalized gradient approximation (GGA) exchange-correlation functional competitive with state-of-the-art GGAs for solids, but also reasonably accurate for large atoms and ordinary chemistry.
Nous avons etendu le domaine d’applicabilite de la theorie des fonctionnelles de la densite au ca... more Nous avons etendu le domaine d’applicabilite de la theorie des fonctionnelles de la densite au cas de systemes relativistes ayant une polarisation da spin. La difficulte de ce cas specifique reside dans le fait que la combinaison de la polarisation de spin avec l’effet spin-orbite brise toute degenerescence du systeme, ce qui implique que ni le moment angulaire total j, ni sa partie orbitale l ne constituent de bons nombres quantiques du systeme. Il s’ensuit que les fonctions d’onde ne peuvent etre exprimees qu’en termes d’une serie infinie d’orbitales de Dirac. Cette difficulte peut toutefois etre contournee : nous indiquons une methode qui permet d’arriver a une solution explicite dans le cas de systemes atomiques et qui est susceptible d’etre appliquee aux solides. Au moyen de cette methode nous avons etudie les proprietes magnetiques des ions trivalents de terres rares. Aussi avons-nous elabore une nouvelle approximation a la partie d’echange de la fonctionnelle energie d’echang...
Journal of Physics: Condensed Matter
The elastic constants of δ-AlOOH have been calculated for applied pressures in the range 0-40 GPa... more The elastic constants of δ-AlOOH have been calculated for applied pressures in the range 0-40 GPa using three exchange-correlation functionals, i.e. PBEsol, TCAsol and PBE. PBEsol and TCAsol, which describe the geometry of this system very well, give similar results, while the PBE values are smaller, a consequence of the fact that the PBE lattice parameters are too large. In agreement with the experiments, the calculations show that at low pressure the axial compressibility is greater in the b direction and smaller in the c direction, while the opposite is true at high pressure. This change takes place 5 GPa before the calculated hydrogen bond symmetrization transition. Combining this result with those reported in the experimental papers, one obtains a strong indication that symmetrization takes place at about 15 GPa, in excellent agreement with the PBEsol and TCAsol predictions.
Theoretical Chemistry Accounts
Dispersion corrections, namely the D3 and VV10 methodologies, have been added to the TCA GGA-like... more Dispersion corrections, namely the D3 and VV10 methodologies, have been added to the TCA GGA-like family of functionals. Without corrections, these functionals give very good results for iono-covalent systems, but they are inferior to other GGAs (e.g., PBE) for weakly interacting complexes. Applying dispersion corrections, this failure is completely overcome. In particular, RevTCA, which is the best functional for iono-covalent systems, becomes the best for weakly interacting complexes too, with mean absolute errors very often smaller than one tenth of {\AA }$$Å for the geometries and 1 kcal/mol for the dissociation energies.
Physical Review B
Unpaired electrons in YTiO 3 ferromagnetic crystal (below 30 K) were studied by polarized neutron... more Unpaired electrons in YTiO 3 ferromagnetic crystal (below 30 K) were studied by polarized neutron diffraction (PND) and incoherent x-ray magnetic Compton scattering (MCS). These experiments provide both position and momentum representations of the electrons at the origin of the magnetic behavior, mostly those in the t 2g state of Ti atoms. A two-dimensional reconstruction was conducted from experimental and theoretical directional magnetic Compton profiles to obtain the two-dimensional magnetic electron momentum density. A "superposition" method is proposed to examine the coherence between results for position and momentum spaces, respectively. This model-free approach allows a straightforward cross-checking of PND and MCS experiments. An "isolated Ti model" is proposed to emphasize the role played by O 1 in the ferromagnetic coupling between Ti and its neighboring atoms.
Journal of Physics: Conference Series
Synopsis Cross sections for vibrational excitation and dissociative electron attachment (DEA) of ... more Synopsis Cross sections for vibrational excitation and dissociative electron attachment (DEA) of the nitrogen dioxide (NO2) molecule in collisions with low-energy electrons are determined theoretically. The thermally-averaged rate coefficients of vibrational excitation are presented for the temperatures from 10 K to 10000 K. The obtained DEA cross section for NO2 agrees well with experimental data.
Physical Review A
Cross sections and rate coefficients for vibrational excitation and de-excitation of the N 2 O mo... more Cross sections and rate coefficients for vibrational excitation and de-excitation of the N 2 O molecule by a low-energy electron for transitions between the lowest vibrational levels are computed using a first-principles approach. The present theoretical approach employs the normal-mode approximation for the description of target vibrational states, the vibrational frame transformation to compute amplitudes of vibrational transitions, and the R-matrix method to compute ab initio electronic bound and continuum states. It was found that the nonadiabatic Renner-Teller effect, which couples partial waves of the incident electron with degenerate bending vibrations of N 2 O, is responsible for the excitation of the bending mode. Theoretical results obtained agree reasonably well with available experimental data at low energies. Thermally averaged rate coefficients are computed for temperatures in the 10-10 000 K range.
Acta Crystallographica Section A Foundations and Advances
One of the goals of Quantum Crystallography is to study to what extent experimental tools of crys... more One of the goals of Quantum Crystallography is to study to what extent experimental tools of crystallography such as X-ray, electron, neutron diffraction, in their polarized and non-polarized versions can be used to gain better access to fundamental quantum properties such as the N-electron wavefunction. In recent years, our collaboration has developed methods to extend the range of scattering experiments to gain access to better one-electron reduced density matrices which fulfill N-representability conditions. Two such possible approaches will be described in the cases of spin-resolved and charge-only 1-RDM for model systems. The purpose is to assess the quality of a 1-RDM reconstruction using coherent-elastic and incoherent-inelastic pseudoexperimental data and critically compare the result to the original, periodic ab-initio derived, 1-RDM standard reference.
Computation
We extend the SG4 generalized gradient approximation, developed for covalent and ionic solids wit... more We extend the SG4 generalized gradient approximation, developed for covalent and ionic solids with a nonlocal van der Waals functional. The resulting SG4-rVV10m functional is tested, considering two possible parameterizations, for various kinds of bulk solids including layered materials and molecular crystals as well as regular bulk materials. The results are compared to those of similar methods, PBE + rVV10L and rVV10. In most cases, SG4-rVV10m yields a quite good description of systems (from iono-covalent to hydrogen-bond and dispersion interactions), being competitive with PBE + rVV10L and rVV10 for dispersion-dominated systems and slightly superior for iono-covalent ones. Thus, it shows a promising applicability for solid-state applications. In a few cases, however, overbinding is observed. This is analysed in terms of gradient contributions to the functional.
Acta Crystallographica Section A Foundations and Advances
Figure 1. ORTEP drawing of the [Fe(C(SiMe 3) 3) 2 ]anion at 100 K. Atoms are depicted as 50 % pro... more Figure 1. ORTEP drawing of the [Fe(C(SiMe 3) 3) 2 ]anion at 100 K. Atoms are depicted as 50 % probability ellipsoids. Orange, petrol blue and grey refer to iron, silicon and carbon, respectively. Hydrogen atoms have been omitted for clarity.
Heat transfer between two silica clusters is investigated by using the nonequilibrium Green's fun... more Heat transfer between two silica clusters is investigated by using the nonequilibrium Green's function method. In the gap range between 4 Å and 3 times the cluster size, the thermal conductance decreases as predicted by the surface charge-charge interaction. Above 5 times the cluster size, the volume dipole-dipole interaction predominates. Finally, when the distance becomes smaller than 4 Å, a quantum interaction where the electrons of both clusters are shared takes place. This quantum interaction leads to the dramatic increase of the thermal coupling between neighbor clusters due to strong interactions. This study finally provides a description of the transition between radiation and heat conduction in gaps smaller than a few nanometers.
Phys Rev B, 1989
In the relativistic extension of the spin-polarized density-functional theory the one-electron wa... more In the relativistic extension of the spin-polarized density-functional theory the one-electron wave functions are the solutions of two coupled Dirac equations. In general, to solve these equations is a difficult task and only a few non-self-consistent solid-state calculations based on them have been performed. It is the purpose of this paper to show that very accurate approximate solutions can be found by solving uncoupled Dirac equations. This gives rise to a method which can be used for generating effective potentials and magnetic fields to be used in the coupled equations, but also to an independent way of performing self-consistent calculations.
Journal of Chemical Theory and Computation, May 29, 2013
A new index is defined with the aim of further exploring the metric of excited electronic states ... more A new index is defined with the aim of further exploring the metric of excited electronic states in the framework of the Time-Dependent Density Functional Theory. This descriptor, called ∆r, is based on the charge centroids of the orbitals involved in the excitations and can be interpreted in term of the hole-electron distance. The tests carried out on a set of molecules characterized by a significant number of charge-transfer excitations well illustrate its ability in discriminating between short (∆r ≤ 1.5 Å) and long-range (∆r ≥ 2.0 Å) excitations. On the basis of the wellknown pitfalls of TD-DFT, its values can be then associated to the functional performances in reproducing different type of transitions, and allow for the definition of a "trust radius" for GGA and hybrid functionals. The study of other systems, including some well-known difficult cases for other metric descriptors, gives further evidence of the high discrimination power of the proposed index. The combined use with other density or orbital-based descriptors is finally suggested to have a reliable diagnostic test of TD-DFT transitions.
Http Www Theses Fr, 2003
Les trois surfaces de plus bas indices de Miller du Cuivre ainsi que la reconstruction de la surf... more Les trois surfaces de plus bas indices de Miller du Cuivre ainsi que la reconstruction de la surface (110) suite a l'adsorption d'oxygene atomique ont ete etudiees dans cette these. Il a fallu pour cela developper les outils necessaires d'une part a la modelisation de la structure des bandes d'energie de ces surfaces et d'autre part a l'ajustement des bandes calculees sur des donnees experimentales obtenues par photo-emission directe et inverse. Cela a ete realise en combinant la methode LCAO empirique d'interpolation de calculs de bandes d'e��nergie des solides et un programme de minimisation de fonctions a plusieurs parametres. Dans la premiere etape, qui a consiste a modeliser un cristal massif ainsi que les principales surfaces propres, nous avons inclus dans le processus d'ajustement des donnees experimentales issues de mesures sur la surface (110), ce qui nous a permis d'obtenir un seul ensemble de parametres decrivant les interactions des atomes dans le Cuivre massif et applicable aux etudes des surfaces. Cet ensemble de parametres a donne une structure de bandes du volume et des surfaces en accord tres pousse avec les donnees experimentales, ce qui n'existait pas jusqu'a present dans la litterature. Nous avons ensuite etabli un deuxieme ensemble de parametres afin de prendre en compte les interactions d'atomes d'oxygene avec un substrat de Cuivre, ce dernier etant decrit par les parametres precedemment obtenus. Nous avons ainsi pu modeliser la structure des bandes de la surface (110) oxydee dans ses plus fins details, et notamment la dispersion et la symetrie des etats anti-liants de l'oxygene, ce qui n'avait jamais ete realise auparavant ni dans le cadre d'une modelisation LCAO, ni dans le cadre de calculs ab-initio. Les applications de ces calculs sont multiples, et tous les travaux menes pour etudier le cristal de Cuivre et ses principales surfaces peuvent etre reconduits pour d'autres metaux de transition.
Journal of Electronic Materials, 2012
Density functional theory and the Boltzmann transport equation were used to calculate the thermoe... more Density functional theory and the Boltzmann transport equation were used to calculate the thermoelectric transport coefficients for bulk V 2 O 5 and MV 2 O 5 (M = Cr, Ti, Na, Li). The structural relaxation for the given compounds based on the ABINIT code was observed. The temperature dependences of the Seebeck coefficients as well as electrical and thermal electrical conductivities of all relaxed structures displayed anisotropic behavior. Electrooptical measurements of thermoelectric properties were carried out on V 2 O 5 thin films obtained by thermal evaporation with different post-annealing treatments. A Seebeck coefficient of À148 lV/K at T = 300 K was obtained in the in-plane direction for V 2 O 5 thin films with thickness less than 100 nm.
Physical Review A, 2019
A theoretical approach for the electron-impact vibronic excitation of molecular ions with low-lyi... more A theoretical approach for the electron-impact vibronic excitation of molecular ions with low-lying excited electronic states is described. In this approach, the fixed-nuclear R-matrix method is employed to compute electron-ion scattering matrices in the Born-Oppenheimer approximation. A vibronic frame transformation and the closed-channel elimination procedure in a spirit of molecular quantum defect theory are employed to construct an energy-dependent scattering matrix describing interactions between vibronic channels of the target ion induced by the incident electron. The obtained scattering matrix accounts for Rydberg series of vibronic resonances in the collisional spectrum. The approach is applied to the CH + ion of an astrophysical and technological interest. Cross sections for vibronic excitation for different combinations of initial and final vibronic states are computed. A good agreement between electronic-excitation cross sections, obtained using the quantum defect theory and in a direct R-matrix calculation, demonstrates that the present approach provides a reliable tool for determination of vibronic (de-)excitation cross sections for targets with low-energy electronic resonances. Such targets were difficult to treat theoretically using earlier methods.
Plasma Sources Science and Technology, 2019
In this study, we compute cross sections for vibrational excitation of NO2 by electron impact. Ca... more In this study, we compute cross sections for vibrational excitation of NO2 by electron impact. Calculations are performed using a theoretical approach based on a combination of the normal mode approximation for vibrational states of the target molecule, fixed-nuclei electron-NO2 scattering matrices and the vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions. Thermally-averaged rate coefficients are derived from the obtained cross sections for temperatures in the 10–10000 K interval for excitation of each normal mode of the target molecule. Analytical fits for the rate coefficients for singlets and triplets are provided. In addition, a comprehensive set of calculations are performed for assessing the uncertainty of the present calculations. The uncertainty assessments indicate that the computed observables for vibrational (de-)excitation is reasonable for later use in NO2-containing plasma kinetics modeling.
Physical Review B, 2016
Using the semiclassical neutral atom theory, we extend to fourth order the modified gradient expa... more Using the semiclassical neutral atom theory, we extend to fourth order the modified gradient expansion of the exchange energy of density functional theory. This expansion can be applied both to large atoms and solid-state problems. Moreover, we show that it can be employed to construct a simple and non-empirical generalized gradient approximation (GGA) exchange-correlation functional competitive with state-of-the-art GGAs for solids, but also reasonably accurate for large atoms and ordinary chemistry.
Nous avons etendu le domaine d’applicabilite de la theorie des fonctionnelles de la densite au ca... more Nous avons etendu le domaine d’applicabilite de la theorie des fonctionnelles de la densite au cas de systemes relativistes ayant une polarisation da spin. La difficulte de ce cas specifique reside dans le fait que la combinaison de la polarisation de spin avec l’effet spin-orbite brise toute degenerescence du systeme, ce qui implique que ni le moment angulaire total j, ni sa partie orbitale l ne constituent de bons nombres quantiques du systeme. Il s’ensuit que les fonctions d’onde ne peuvent etre exprimees qu’en termes d’une serie infinie d’orbitales de Dirac. Cette difficulte peut toutefois etre contournee : nous indiquons une methode qui permet d’arriver a une solution explicite dans le cas de systemes atomiques et qui est susceptible d’etre appliquee aux solides. Au moyen de cette methode nous avons etudie les proprietes magnetiques des ions trivalents de terres rares. Aussi avons-nous elabore une nouvelle approximation a la partie d’echange de la fonctionnelle energie d’echang...
Journal of Physics: Condensed Matter
The elastic constants of δ-AlOOH have been calculated for applied pressures in the range 0-40 GPa... more The elastic constants of δ-AlOOH have been calculated for applied pressures in the range 0-40 GPa using three exchange-correlation functionals, i.e. PBEsol, TCAsol and PBE. PBEsol and TCAsol, which describe the geometry of this system very well, give similar results, while the PBE values are smaller, a consequence of the fact that the PBE lattice parameters are too large. In agreement with the experiments, the calculations show that at low pressure the axial compressibility is greater in the b direction and smaller in the c direction, while the opposite is true at high pressure. This change takes place 5 GPa before the calculated hydrogen bond symmetrization transition. Combining this result with those reported in the experimental papers, one obtains a strong indication that symmetrization takes place at about 15 GPa, in excellent agreement with the PBEsol and TCAsol predictions.
Theoretical Chemistry Accounts
Dispersion corrections, namely the D3 and VV10 methodologies, have been added to the TCA GGA-like... more Dispersion corrections, namely the D3 and VV10 methodologies, have been added to the TCA GGA-like family of functionals. Without corrections, these functionals give very good results for iono-covalent systems, but they are inferior to other GGAs (e.g., PBE) for weakly interacting complexes. Applying dispersion corrections, this failure is completely overcome. In particular, RevTCA, which is the best functional for iono-covalent systems, becomes the best for weakly interacting complexes too, with mean absolute errors very often smaller than one tenth of {\AA }$$Å for the geometries and 1 kcal/mol for the dissociation energies.
Physical Review B
Unpaired electrons in YTiO 3 ferromagnetic crystal (below 30 K) were studied by polarized neutron... more Unpaired electrons in YTiO 3 ferromagnetic crystal (below 30 K) were studied by polarized neutron diffraction (PND) and incoherent x-ray magnetic Compton scattering (MCS). These experiments provide both position and momentum representations of the electrons at the origin of the magnetic behavior, mostly those in the t 2g state of Ti atoms. A two-dimensional reconstruction was conducted from experimental and theoretical directional magnetic Compton profiles to obtain the two-dimensional magnetic electron momentum density. A "superposition" method is proposed to examine the coherence between results for position and momentum spaces, respectively. This model-free approach allows a straightforward cross-checking of PND and MCS experiments. An "isolated Ti model" is proposed to emphasize the role played by O 1 in the ferromagnetic coupling between Ti and its neighboring atoms.
Journal of Physics: Conference Series
Synopsis Cross sections for vibrational excitation and dissociative electron attachment (DEA) of ... more Synopsis Cross sections for vibrational excitation and dissociative electron attachment (DEA) of the nitrogen dioxide (NO2) molecule in collisions with low-energy electrons are determined theoretically. The thermally-averaged rate coefficients of vibrational excitation are presented for the temperatures from 10 K to 10000 K. The obtained DEA cross section for NO2 agrees well with experimental data.
Physical Review A
Cross sections and rate coefficients for vibrational excitation and de-excitation of the N 2 O mo... more Cross sections and rate coefficients for vibrational excitation and de-excitation of the N 2 O molecule by a low-energy electron for transitions between the lowest vibrational levels are computed using a first-principles approach. The present theoretical approach employs the normal-mode approximation for the description of target vibrational states, the vibrational frame transformation to compute amplitudes of vibrational transitions, and the R-matrix method to compute ab initio electronic bound and continuum states. It was found that the nonadiabatic Renner-Teller effect, which couples partial waves of the incident electron with degenerate bending vibrations of N 2 O, is responsible for the excitation of the bending mode. Theoretical results obtained agree reasonably well with available experimental data at low energies. Thermally averaged rate coefficients are computed for temperatures in the 10-10 000 K range.
Acta Crystallographica Section A Foundations and Advances
One of the goals of Quantum Crystallography is to study to what extent experimental tools of crys... more One of the goals of Quantum Crystallography is to study to what extent experimental tools of crystallography such as X-ray, electron, neutron diffraction, in their polarized and non-polarized versions can be used to gain better access to fundamental quantum properties such as the N-electron wavefunction. In recent years, our collaboration has developed methods to extend the range of scattering experiments to gain access to better one-electron reduced density matrices which fulfill N-representability conditions. Two such possible approaches will be described in the cases of spin-resolved and charge-only 1-RDM for model systems. The purpose is to assess the quality of a 1-RDM reconstruction using coherent-elastic and incoherent-inelastic pseudoexperimental data and critically compare the result to the original, periodic ab-initio derived, 1-RDM standard reference.
Computation
We extend the SG4 generalized gradient approximation, developed for covalent and ionic solids wit... more We extend the SG4 generalized gradient approximation, developed for covalent and ionic solids with a nonlocal van der Waals functional. The resulting SG4-rVV10m functional is tested, considering two possible parameterizations, for various kinds of bulk solids including layered materials and molecular crystals as well as regular bulk materials. The results are compared to those of similar methods, PBE + rVV10L and rVV10. In most cases, SG4-rVV10m yields a quite good description of systems (from iono-covalent to hydrogen-bond and dispersion interactions), being competitive with PBE + rVV10L and rVV10 for dispersion-dominated systems and slightly superior for iono-covalent ones. Thus, it shows a promising applicability for solid-state applications. In a few cases, however, overbinding is observed. This is analysed in terms of gradient contributions to the functional.
Acta Crystallographica Section A Foundations and Advances
Figure 1. ORTEP drawing of the [Fe(C(SiMe 3) 3) 2 ]anion at 100 K. Atoms are depicted as 50 % pro... more Figure 1. ORTEP drawing of the [Fe(C(SiMe 3) 3) 2 ]anion at 100 K. Atoms are depicted as 50 % probability ellipsoids. Orange, petrol blue and grey refer to iron, silicon and carbon, respectively. Hydrogen atoms have been omitted for clarity.
Heat transfer between two silica clusters is investigated by using the nonequilibrium Green's fun... more Heat transfer between two silica clusters is investigated by using the nonequilibrium Green's function method. In the gap range between 4 Å and 3 times the cluster size, the thermal conductance decreases as predicted by the surface charge-charge interaction. Above 5 times the cluster size, the volume dipole-dipole interaction predominates. Finally, when the distance becomes smaller than 4 Å, a quantum interaction where the electrons of both clusters are shared takes place. This quantum interaction leads to the dramatic increase of the thermal coupling between neighbor clusters due to strong interactions. This study finally provides a description of the transition between radiation and heat conduction in gaps smaller than a few nanometers.
Phys Rev B, 1989
In the relativistic extension of the spin-polarized density-functional theory the one-electron wa... more In the relativistic extension of the spin-polarized density-functional theory the one-electron wave functions are the solutions of two coupled Dirac equations. In general, to solve these equations is a difficult task and only a few non-self-consistent solid-state calculations based on them have been performed. It is the purpose of this paper to show that very accurate approximate solutions can be found by solving uncoupled Dirac equations. This gives rise to a method which can be used for generating effective potentials and magnetic fields to be used in the coupled equations, but also to an independent way of performing self-consistent calculations.
Journal of Chemical Theory and Computation, May 29, 2013
A new index is defined with the aim of further exploring the metric of excited electronic states ... more A new index is defined with the aim of further exploring the metric of excited electronic states in the framework of the Time-Dependent Density Functional Theory. This descriptor, called ∆r, is based on the charge centroids of the orbitals involved in the excitations and can be interpreted in term of the hole-electron distance. The tests carried out on a set of molecules characterized by a significant number of charge-transfer excitations well illustrate its ability in discriminating between short (∆r ≤ 1.5 Å) and long-range (∆r ≥ 2.0 Å) excitations. On the basis of the wellknown pitfalls of TD-DFT, its values can be then associated to the functional performances in reproducing different type of transitions, and allow for the definition of a "trust radius" for GGA and hybrid functionals. The study of other systems, including some well-known difficult cases for other metric descriptors, gives further evidence of the high discrimination power of the proposed index. The combined use with other density or orbital-based descriptors is finally suggested to have a reliable diagnostic test of TD-DFT transitions.