Fabien Gatti | Université Paris-Saclay / UPSaclay (original) (raw)
Papers by Fabien Gatti
arXiv (Cornell University), Apr 7, 2022
The transfer of a hydrated proton between water molecules in aqueous solution is accompanied by t... more The transfer of a hydrated proton between water molecules in aqueous solution is accompanied by the large-scale structural reorganization of the environment as the proton relocates, giving rise to the Grotthus mechanism. 1 The Zundel (H 5 O + 2) and Eigen (H 9 O + 4) 1 arXiv:2204.03744v1 [physics.chem-ph] 7 Apr 2022 M.S., H.-D.M. and O.V. conceived the idea and planed the calculations and the analysis methodology. M.S. contributed the SOP fitting of the PES and DMS and performed the dynamical calculations and analysis. F.G., D.L. and O.V. designed the coordinates system. F.G. and D.L.
Journal of Chemical Physics, Oct 8, 2008
The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational... more The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational energy redistribution in HFCO and DFCO. In contrast to our previous studies [Pasin et al., J. Chem. Phys. 124, 194304 (2006) and 126, 024302 (2007)], the dynamics is now performed in the presence of an external time-dependent field. This more closely reflects the experimental conditions. A six-dimensional dipole surface is computed. The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. Special emphasis is placed on the excitation of the out-of-plane bending vibration and on the dissociation of the molecule. In the case of DFCO, we predict that it is possible to excite the out-of-plane bending mode of vibration and to drive the dissociation to DF+CO with only one laser pulse with a fixed frequency and without excitation of an electronic state.
Springer eBooks, Dec 17, 2007
For the understanding of physical processes on a molecular scale it is convenient to study the un... more For the understanding of physical processes on a molecular scale it is convenient to study the underlying dynamics by wavepacket propagation. Many different propagation schemes have been developed in the past, reaching from the numerically exact standard method, that can only treat very small systems to approximate ones like the time dependent Hartree method (TDH). One of those methods, the
Chemical Physics Letters, 2017
The inelastic scattering between a rigid rotor triatomic molecule and an atom is described within... more The inelastic scattering between a rigid rotor triatomic molecule and an atom is described within the frame of the MultiConfiguration Time dependent Hartree (MCTDH) method. Sample calculations are done on the H 2 OAr system for which a flexible 6D PES (used here in the rigid rotor approximation) has been recently computed in our group and will be presented separately. The results are compared with corresponding time independent calculations using the Arthurs and Dalgarno approach and confirm as expected the equivalence of the two methods.
Journal of Chemical Physics, Aug 25, 2020
We report a large set of state-to-state rate constants for the H + HD reactive collision, using Q... more We report a large set of state-to-state rate constants for the H + HD reactive collision, using Quasi-Classical Trajectory (QCT) simulations on the accurate H 3 global potential energy surface of Mielke et al. [J. Chem. Phys. 116, 4142 (2002)]. High relative collision energies (up to ≈56 000 K) and high rovibrational levels of HD (up to ≈50 000 K), relevant to various non thermal equilibrium astrophysical media, are considered. We have validated the accuracy of our QCT calculations with a new efficient adaptation of the Multi Configuration Time Dependent Hartree (MCTDH) method to compute the reaction probability of a specific reactive channel. Our study has revealed that the high temperature regime favors the production of H 2 in its highly rovibrationnally excited states, which can de-excite radiatively (cooling the gas) or collisionally (heating the gas). Those new state-to-state QCT reaction rate constants represent a significant improvement in our understanding of the possible mechanisms leading to the destruction of HD by its collision with a H atom.
Journal of Chemical Theory and Computation, Jul 15, 2022
Conventional quantum mechanical characterization of photodissociation dynamics is restricted by s... more Conventional quantum mechanical characterization of photodissociation dynamics is restricted by steep scaling laws with respect to the dimensionality of the system. In this work, we examine the applicability of the multi-configurational time-dependent Hartree (MCTDH) method in treating nonadiabatic photodissociation dynamics in two prototypical systems, taking advantage of its favorable scaling laws. To conform to the sum-of-product form, elements of the ab initio diabatic potential energy matrix (DPEM) are re-expressed using the recently proposed Monte Carlo canonical polyadic decomposition method, with enforcement of proper symmetry. The MCTDH absorption spectra and product branching ratios are shown to compare well with those calculated using conventional grid-based methods, demonstrating its promise for treating high-dimensional nonadiabatic photodissociation problems.
Lecture notes in chemistry, 2017
In the present book, we will consider molecular systems either isolated or in interaction with ex... more In the present book, we will consider molecular systems either isolated or in interaction with external electromagnetic fields. In a bottom-up approach, which we will try to follow here, a molecule, or more generally a molecular system, is regarded as a collection of electrons and nuclei in interaction with each other and possibly with external fields.
Lecture notes in chemistry, 2017
In the previous applications, we have considered only “artificial” wavepackets, i.e. wavepackets ... more In the previous applications, we have considered only “artificial” wavepackets, i.e. wavepackets that generally do not correspond to any realistic experimental situation. The mathematical properties of the wavepackets allowed us to obtain absorption spectra and cross sections including all the quantum effect that can impact a molecular process. All the systems were assumed to be isolated and no quantum decoherence occurred during the propagations of the wavepackets. However, wavepackets are not only mathematical tools to obtain some measured physical quantities, they can be created experimentally. Since the advent of lasers, coherent sources of light can be produced that can in turn create coherent superpositions of molecular states and thus molecular wavepackets. Quantum coherence will finally be dissipated by interaction with the environment but, before this, quantum coherence may be preserved during a time that is sufficient to trigger a new type of chemical process.
Journal of Chemical Physics, Nov 7, 2010
Vibrationally mediated photodissociation of NH 3 and ND 3 in the A band allows the exploration of... more Vibrationally mediated photodissociation of NH 3 and ND 3 in the A band allows the exploration of the excited-state potential energy surface in regions that are not accessible from the ground vibrational state of these polyatomic systems. Using our recently developed coupled ab initio potential energy surfaces in a quasi-diabatic representation, we report here a full-dimensional quantum characterization of the Ã← X̃absorption spectra for vibrationally excited NH 3 and ND 3 and the corresponding nonadiabatic dissociation dynamics into the NH 2 (Ã2A 1) + H and NH 2 (X̃2B 1) + H channels. The predissociative resonances in the absorption spectra have been assigned with appropriate quantum numbers. The NH 2 (Ã2A 1)/NH 2 (X̃2B 1) branching ratio was found to be mildly sensitive to the initial vibrational excitation prior to photolysis. Implications for interpreting experimental data are discussed.
Journal of Chemical Physics, Nov 27, 2013
We develop a new general code to automatically derive exact analytical kinetic energy operators i... more We develop a new general code to automatically derive exact analytical kinetic energy operators in terms of polyspherical coordinates. Computer procedures based on symbolic calculations are implemented. Sets of orthogonal or non-orthogonal vectors are used to parametrize the molecular systems in space. For each set of vectors, and whatever the size of the system, the exact analytical kinetic energy operator (including the overall rotation and the Coriolis coupling) can be derived by the program. The correctness of the implementation is tested for different sets of vectors and for several systems of various sizes.
Lecture notes in chemistry, 2017
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Journal of Chemical Physics, Mar 16, 2004
Using a full six-dimensional ab initio potential energy surface and nuclear motion Hamiltonian, t... more Using a full six-dimensional ab initio potential energy surface and nuclear motion Hamiltonian, time-dependent computations were performed for the cis-trans isomerization of HONO. The multiconfiguration time-dependent Hartree method was used to propagate the six-dimensional wave packets. The initial excitations were chosen to be excitations of the local stretch modes and the HON local bend mode. The energy redistribution within 2 to 5 ps in the energy region of the OH stretching modes in both isomers was analyzed. The Fourier transformed frequency domain spectra were attributed to the eigenstates calculated previously by the time-independent variational approach. The results are also compared with classical trajectory computations of Thomson et al. [J. Chem. Phys. 118, 1673 (2003)] on empirical surfaces. In agreement with matrix experiments, the cis→trans isomerization was found to be much faster than the opposite interconversion. The intramolecular dynamics were found to be very complex involving numerous weakly excited delocalized eigenstates and anharmonic resonances. Particularly in the cis-isomer, the excitation of the HON bending local mode leads to fast energy redistribution in cis-trans delocalized modes. Neither the excitation of the OH stretching local mode in the cis nor in the trans form produces a fast isomerization, in agreement with the strongly localized characters of the corresponding eigenstates calculated variationally by Richter et al. [J. Chem. Phys. 120, 1306 (2004)] and the gas phase spectra of HONO.
Journal of Chemical Physics, Jun 1, 1998
Within the framework of adapted coupled-angular-momentum spectral representations, the geometrica... more Within the framework of adapted coupled-angular-momentum spectral representations, the geometrical description of a four-atom molecular system by three Jacobi relative position vectors is shown to result in matrices representing the kinetic energy operator, prediagonalized to a very large extent. A fully diagonal representation is built for the angular (internal and rotational) part of the problem.
Journal of Chemical Physics, Jun 16, 2009
Quantum dynamical calculations are reported for the zero point energy, several low-lying vibratio... more Quantum dynamical calculations are reported for the zero point energy, several low-lying vibrational states, and the infrared spectrum of the H 5 O 2 + cation. The calculations are performed by the multiconfiguration time-dependent Hartree ͑MCTDH͒ method. A new vector parametrization based on a mixed Jacobi-valence description of the system is presented. With this parametrization the potential energy surface coupling is reduced with respect to a full Jacobi description, providing a better convergence of the n-mode representation of the potential. However, new coupling terms appear in the kinetic energy operator. These terms are derived and discussed. A mode-combination scheme based on six combined coordinates is used, and the representation of the 15-dimensional potential in terms of a six-combined mode cluster expansion including up to some 7-dimensional grids is discussed. A statistical analysis of the accuracy of the n-mode representation of the potential at all orders is performed. Benchmark, fully converged results are reported for the zero point energy, which lie within the statistical uncertainty of the reference diffusion Monte Carlo result for this system. Some low-lying vibrationally excited eigenstates are computed by block improved relaxation, illustrating the applicability of the approach to large systems. Benchmark calculations of the linear infrared spectrum are provided, and convergence with increasing size of the time-dependent basis and as a function of the order of the n-mode representation is studied. The calculations presented here make use of recent developments in the parallel version of the MCTDH code, which are briefly discussed. We also show that the infrared spectrum can be computed, to a very good approximation, within D 2d symmetry, instead of the G 16 symmetry used before, in which the complete rotation of one water molecule with respect to the other is allowed, thus simplifying the dynamical problem.
Journal of Chemical Physics, Jul 17, 2009
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
Journal of Chemical Physics, Nov 14, 2007
Journal of Chemical Physics, Nov 14, 2007
The infrared absorption spectrum of the protonated water dimer (H 5 O + 2) is simulated in full d... more The infrared absorption spectrum of the protonated water dimer (H 5 O + 2) is simulated in full dimensionality (15D) in the spectral range 0-4000 cm −1. The calculations are performed using the Multiconfiguration Time-Dependent Hartree (MCTDH) method for propagation of wavepackets. All the fundamentals and several overtones of the vibrational motion are computed. The spectrum of H 5 O + 2 is shaped to a large extent by couplings of the proton-transfer motion to large amplitude
Lecture notes in chemistry, 2017
Lecture notes in chemistry, 2017
arXiv (Cornell University), Apr 7, 2022
The transfer of a hydrated proton between water molecules in aqueous solution is accompanied by t... more The transfer of a hydrated proton between water molecules in aqueous solution is accompanied by the large-scale structural reorganization of the environment as the proton relocates, giving rise to the Grotthus mechanism. 1 The Zundel (H 5 O + 2) and Eigen (H 9 O + 4) 1 arXiv:2204.03744v1 [physics.chem-ph] 7 Apr 2022 M.S., H.-D.M. and O.V. conceived the idea and planed the calculations and the analysis methodology. M.S. contributed the SOP fitting of the PES and DMS and performed the dynamical calculations and analysis. F.G., D.L. and O.V. designed the coordinates system. F.G. and D.L.
Journal of Chemical Physics, Oct 8, 2008
The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational... more The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational energy redistribution in HFCO and DFCO. In contrast to our previous studies [Pasin et al., J. Chem. Phys. 124, 194304 (2006) and 126, 024302 (2007)], the dynamics is now performed in the presence of an external time-dependent field. This more closely reflects the experimental conditions. A six-dimensional dipole surface is computed. The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. Special emphasis is placed on the excitation of the out-of-plane bending vibration and on the dissociation of the molecule. In the case of DFCO, we predict that it is possible to excite the out-of-plane bending mode of vibration and to drive the dissociation to DF+CO with only one laser pulse with a fixed frequency and without excitation of an electronic state.
Springer eBooks, Dec 17, 2007
For the understanding of physical processes on a molecular scale it is convenient to study the un... more For the understanding of physical processes on a molecular scale it is convenient to study the underlying dynamics by wavepacket propagation. Many different propagation schemes have been developed in the past, reaching from the numerically exact standard method, that can only treat very small systems to approximate ones like the time dependent Hartree method (TDH). One of those methods, the
Chemical Physics Letters, 2017
The inelastic scattering between a rigid rotor triatomic molecule and an atom is described within... more The inelastic scattering between a rigid rotor triatomic molecule and an atom is described within the frame of the MultiConfiguration Time dependent Hartree (MCTDH) method. Sample calculations are done on the H 2 OAr system for which a flexible 6D PES (used here in the rigid rotor approximation) has been recently computed in our group and will be presented separately. The results are compared with corresponding time independent calculations using the Arthurs and Dalgarno approach and confirm as expected the equivalence of the two methods.
Journal of Chemical Physics, Aug 25, 2020
We report a large set of state-to-state rate constants for the H + HD reactive collision, using Q... more We report a large set of state-to-state rate constants for the H + HD reactive collision, using Quasi-Classical Trajectory (QCT) simulations on the accurate H 3 global potential energy surface of Mielke et al. [J. Chem. Phys. 116, 4142 (2002)]. High relative collision energies (up to ≈56 000 K) and high rovibrational levels of HD (up to ≈50 000 K), relevant to various non thermal equilibrium astrophysical media, are considered. We have validated the accuracy of our QCT calculations with a new efficient adaptation of the Multi Configuration Time Dependent Hartree (MCTDH) method to compute the reaction probability of a specific reactive channel. Our study has revealed that the high temperature regime favors the production of H 2 in its highly rovibrationnally excited states, which can de-excite radiatively (cooling the gas) or collisionally (heating the gas). Those new state-to-state QCT reaction rate constants represent a significant improvement in our understanding of the possible mechanisms leading to the destruction of HD by its collision with a H atom.
Journal of Chemical Theory and Computation, Jul 15, 2022
Conventional quantum mechanical characterization of photodissociation dynamics is restricted by s... more Conventional quantum mechanical characterization of photodissociation dynamics is restricted by steep scaling laws with respect to the dimensionality of the system. In this work, we examine the applicability of the multi-configurational time-dependent Hartree (MCTDH) method in treating nonadiabatic photodissociation dynamics in two prototypical systems, taking advantage of its favorable scaling laws. To conform to the sum-of-product form, elements of the ab initio diabatic potential energy matrix (DPEM) are re-expressed using the recently proposed Monte Carlo canonical polyadic decomposition method, with enforcement of proper symmetry. The MCTDH absorption spectra and product branching ratios are shown to compare well with those calculated using conventional grid-based methods, demonstrating its promise for treating high-dimensional nonadiabatic photodissociation problems.
Lecture notes in chemistry, 2017
In the present book, we will consider molecular systems either isolated or in interaction with ex... more In the present book, we will consider molecular systems either isolated or in interaction with external electromagnetic fields. In a bottom-up approach, which we will try to follow here, a molecule, or more generally a molecular system, is regarded as a collection of electrons and nuclei in interaction with each other and possibly with external fields.
Lecture notes in chemistry, 2017
In the previous applications, we have considered only “artificial” wavepackets, i.e. wavepackets ... more In the previous applications, we have considered only “artificial” wavepackets, i.e. wavepackets that generally do not correspond to any realistic experimental situation. The mathematical properties of the wavepackets allowed us to obtain absorption spectra and cross sections including all the quantum effect that can impact a molecular process. All the systems were assumed to be isolated and no quantum decoherence occurred during the propagations of the wavepackets. However, wavepackets are not only mathematical tools to obtain some measured physical quantities, they can be created experimentally. Since the advent of lasers, coherent sources of light can be produced that can in turn create coherent superpositions of molecular states and thus molecular wavepackets. Quantum coherence will finally be dissipated by interaction with the environment but, before this, quantum coherence may be preserved during a time that is sufficient to trigger a new type of chemical process.
Journal of Chemical Physics, Nov 7, 2010
Vibrationally mediated photodissociation of NH 3 and ND 3 in the A band allows the exploration of... more Vibrationally mediated photodissociation of NH 3 and ND 3 in the A band allows the exploration of the excited-state potential energy surface in regions that are not accessible from the ground vibrational state of these polyatomic systems. Using our recently developed coupled ab initio potential energy surfaces in a quasi-diabatic representation, we report here a full-dimensional quantum characterization of the Ã← X̃absorption spectra for vibrationally excited NH 3 and ND 3 and the corresponding nonadiabatic dissociation dynamics into the NH 2 (Ã2A 1) + H and NH 2 (X̃2B 1) + H channels. The predissociative resonances in the absorption spectra have been assigned with appropriate quantum numbers. The NH 2 (Ã2A 1)/NH 2 (X̃2B 1) branching ratio was found to be mildly sensitive to the initial vibrational excitation prior to photolysis. Implications for interpreting experimental data are discussed.
Journal of Chemical Physics, Nov 27, 2013
We develop a new general code to automatically derive exact analytical kinetic energy operators i... more We develop a new general code to automatically derive exact analytical kinetic energy operators in terms of polyspherical coordinates. Computer procedures based on symbolic calculations are implemented. Sets of orthogonal or non-orthogonal vectors are used to parametrize the molecular systems in space. For each set of vectors, and whatever the size of the system, the exact analytical kinetic energy operator (including the overall rotation and the Coriolis coupling) can be derived by the program. The correctness of the implementation is tested for different sets of vectors and for several systems of various sizes.
Lecture notes in chemistry, 2017
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Journal of Chemical Physics, Mar 16, 2004
Using a full six-dimensional ab initio potential energy surface and nuclear motion Hamiltonian, t... more Using a full six-dimensional ab initio potential energy surface and nuclear motion Hamiltonian, time-dependent computations were performed for the cis-trans isomerization of HONO. The multiconfiguration time-dependent Hartree method was used to propagate the six-dimensional wave packets. The initial excitations were chosen to be excitations of the local stretch modes and the HON local bend mode. The energy redistribution within 2 to 5 ps in the energy region of the OH stretching modes in both isomers was analyzed. The Fourier transformed frequency domain spectra were attributed to the eigenstates calculated previously by the time-independent variational approach. The results are also compared with classical trajectory computations of Thomson et al. [J. Chem. Phys. 118, 1673 (2003)] on empirical surfaces. In agreement with matrix experiments, the cis→trans isomerization was found to be much faster than the opposite interconversion. The intramolecular dynamics were found to be very complex involving numerous weakly excited delocalized eigenstates and anharmonic resonances. Particularly in the cis-isomer, the excitation of the HON bending local mode leads to fast energy redistribution in cis-trans delocalized modes. Neither the excitation of the OH stretching local mode in the cis nor in the trans form produces a fast isomerization, in agreement with the strongly localized characters of the corresponding eigenstates calculated variationally by Richter et al. [J. Chem. Phys. 120, 1306 (2004)] and the gas phase spectra of HONO.
Journal of Chemical Physics, Jun 1, 1998
Within the framework of adapted coupled-angular-momentum spectral representations, the geometrica... more Within the framework of adapted coupled-angular-momentum spectral representations, the geometrical description of a four-atom molecular system by three Jacobi relative position vectors is shown to result in matrices representing the kinetic energy operator, prediagonalized to a very large extent. A fully diagonal representation is built for the angular (internal and rotational) part of the problem.
Journal of Chemical Physics, Jun 16, 2009
Quantum dynamical calculations are reported for the zero point energy, several low-lying vibratio... more Quantum dynamical calculations are reported for the zero point energy, several low-lying vibrational states, and the infrared spectrum of the H 5 O 2 + cation. The calculations are performed by the multiconfiguration time-dependent Hartree ͑MCTDH͒ method. A new vector parametrization based on a mixed Jacobi-valence description of the system is presented. With this parametrization the potential energy surface coupling is reduced with respect to a full Jacobi description, providing a better convergence of the n-mode representation of the potential. However, new coupling terms appear in the kinetic energy operator. These terms are derived and discussed. A mode-combination scheme based on six combined coordinates is used, and the representation of the 15-dimensional potential in terms of a six-combined mode cluster expansion including up to some 7-dimensional grids is discussed. A statistical analysis of the accuracy of the n-mode representation of the potential at all orders is performed. Benchmark, fully converged results are reported for the zero point energy, which lie within the statistical uncertainty of the reference diffusion Monte Carlo result for this system. Some low-lying vibrationally excited eigenstates are computed by block improved relaxation, illustrating the applicability of the approach to large systems. Benchmark calculations of the linear infrared spectrum are provided, and convergence with increasing size of the time-dependent basis and as a function of the order of the n-mode representation is studied. The calculations presented here make use of recent developments in the parallel version of the MCTDH code, which are briefly discussed. We also show that the infrared spectrum can be computed, to a very good approximation, within D 2d symmetry, instead of the G 16 symmetry used before, in which the complete rotation of one water molecule with respect to the other is allowed, thus simplifying the dynamical problem.
Journal of Chemical Physics, Jul 17, 2009
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
Journal of Chemical Physics, Nov 14, 2007
Journal of Chemical Physics, Nov 14, 2007
The infrared absorption spectrum of the protonated water dimer (H 5 O + 2) is simulated in full d... more The infrared absorption spectrum of the protonated water dimer (H 5 O + 2) is simulated in full dimensionality (15D) in the spectral range 0-4000 cm −1. The calculations are performed using the Multiconfiguration Time-Dependent Hartree (MCTDH) method for propagation of wavepackets. All the fundamentals and several overtones of the vibrational motion are computed. The spectrum of H 5 O + 2 is shaped to a large extent by couplings of the proton-transfer motion to large amplitude
Lecture notes in chemistry, 2017
Lecture notes in chemistry, 2017