100 research outputs found
Quantum dynamics in macrosystems with several coupled electronic states: hierarchy of effective Hamiltonians
We address the nonadiabatic quantum dynamics of macrosystems with several
coupled electronic states, taking into account the possibility of multi-state
conical intersections. The general situation of an arbitrary number of states
and arbitrary number of nuclear degrees of freedom (modes) is considered. The
macrosystem is decomposed into a system part carrying a few, strongly coupled
modes, and an environment, comprising the vast number of remaining modes. By
successively transforming the modes of the environment, a hierarchy of
effective Hamiltonians for the environment is constructed. Each effective
Hamiltonian depends on a reduced number of effective modes, which carry
cumulative effects. By considering the system's Hamiltonian along with a few
members of the hierarchy, it is shown mathematically by a moment analysis that
the quantum dynamics of the entire macrosystem can be numerically exactly
computed on a given time-scale. The time scale wanted defines the number of
effective Hamiltonians to be included. The contribution of the environment to
the quantum dynamics of the macrosystem translates into a sequential coupling
of effective modes. The wavefunction of the macrosystem is known in the full
space of modes, allowing for the evaluation of observables such as the
time-dependent individual excitation along modes of interest, as well a spectra
and electronic-population dynamics
Exciton dissociation at donor-acceptor polymer heterojunctions: quantum nonadiabatic dynamics and effective-mode analysis
The quantum-dynamical mechanism of photoinduced subpicosecond exciton
dissociation and the concomitant formation of a charge-separated state at a
TFB:F8BT polymer heterojunction is elucidated. The analysis is based upon a
two-state vibronic coupling Hamiltonian including an explicit 24-mode
representation of a phonon bath comprising high-frequency (CC stretch) and
low-frequency (torsional) modes. The initial relaxation behavior is
characterized by coherent oscillations, along with the decay through an
extended nonadiabatic coupling region. This region is located in the vicinity
of a conical intersection hypersurface. A central ingredient of the analysis is
a novel effective mode representation, which highlights the role of the
low-frequency modes in the nonadiabatic dynamics. Quantum dynamical simulations
were carried out using the multiconfiguration time-dependent Hartree (MCTDH)
method
Interstate Vibronic Coupling Constants Between Electronic Excited States for Complex Molecules
In the construction of diabatic vibronic Hamiltonians for quantum dynamics in
the excited-state manifold of molecules, the coupling constants are often
extracted solely from information on the excited-state energies. Here, a new
protocol is applied to get access to the interstate vibronic coupling constants
at the time-dependent density functional theory level through the overlap
integrals between excited-state adiabatic auxiliary wavefunctions. We discuss
the advantages of such method and its potential for future applications to
address complex systems, in particular those where multiple electronic states
are energetically closely lying and interact. As examples, we apply the
protocol to the study of prototype rhenium carbonyl complexes
[Re(CO)(N,N)(L)] for which non-adiabatic quantum dynamics within the
linear vibronic coupling model and including spin-orbit coupling have been
reported recently.Comment: 36 pages, 7 figures, 4 table
Interstate vibronic coupling constants between electronic excited states for complex molecules
In the construction of diabatic vibronic Hamiltonians for quantum dynamics in the excited-state manifold of molecules, the coupling constants are often extracted solely from information on the excited-state energies. Here, a new protocol is applied to get access to the interstate vibronic coupling constants at the time-dependent density functional theory level through the overlap integrals between excited-state adiabatic auxiliary wavefunctions. We discuss the advantages of such method and its potential for future applications to address complex systems, in particular, those where multiple electronic states are energetically closely lying and interact. We apply the protocol to the study of prototype rhenium carbonyl complexes [Re(CO)3(N,N)(L)]n+ for which non-adiabatic quantum dynamics within the linear vibronic coupling model and including spin-orbit coupling have been reported recently
Spin-dependent Bohm trajectories associated with an electronic transition in hydrogen
The Bohm causal theory of quantum mechanics with spin-dependence is used to
determine electron trajectories when a hydrogen atom is subjected to
(semi-classical) radiation. The transition between the 1s ground state and the
2p0 state is examined. It is found that transitions can be identified along
Bohm trajectories. The trajectories lie on invariant hyperboloid surfaces of
revolution in R^3. The energy along the trajectories is also discussed in
relation to the hydrogen energy eigenvalues.Comment: 18 pages, 8 figure
Conditional Born–Oppenheimer Dynamics: Quantum Dynamics Simulations for the Model Porphine
Computational Improvements to Quantum Wave Packet ab Initio Molecular Dynamics Using a Potential-Adapted, Time-Dependent Deterministic Sampling Technique
Utilisation des trajectoires quantiques dans des processus dynamiques moléculaires
The subject of this mainly methodological thesis is the use of quantum trajectories, defined by de Broglie and Bohm, in studing molecular dynamical processes. Two kind of studies are presented. On the first hand, we use the quantum trajectories to solve the hydrodynamical form of the Schrödinger equation. A numerical method which combine the use of a fixed grid and moving grids was developed and applied to the photodissociation of the H2 molecule. This method is numerically efficient, especially for process like direct dissociation. On the second hand, we use quantum trajectories to establish a new hybrid quantum / classical propagation scheme. Methods of this kind are useful to treat the dynamics of systems too large to be treated by quantum mechanics, but where however at least some degrees of freedom require a quantum treatment. In our method, the positions associated with the quantum trajectories are used in the equation for the classical degrees of freedom to calculate their reaction to the quantum part. The results obtained on three systems, simple enough to have access to the exact results, are compared to those obtained by other hybrid schemes already widely used.La thématique générale de cette thèse essentiellement méthodologique est l'utilisation des trajectoires quantiques, définies par de Broglie et Bohm, dans l'étude de processus dynamiques moléculaires. Deux types d'études seront présentés. Dans la première, nous avons utilisé les trajectoires quantiques pour résoudre la forme hydrodynamique de l'équation de Schrödinger. Une méthode numérique qui combine l'utilisation d'une grille fixe et de grilles mobiles dans le temps a été développée et appliquée à la photodissociation de la molécule H2. Cette méthode peut permettre un gain de temps de calcul et d'espace mémoire, surtout dans des processus comme la dissociation directe. Deuxièmement, nous avons utilisé les trajectoires quantiques pour établir une nouvelle méthode mixte classique / quantique. Ce type de méthode s'avère utile pour traiter la dynamique de systèmes trop grands pour avoir accès à des résultats quantiques exacts, et dans lesquels certains degrés de liberté nécessitent néanmoins un traitement quantique. Dans notre méthode, les positions des trajectoires quantiques interviennent dans les équations des variables classiques du système dans la force que ces dernières ressent. Les résultats obtenus par cette méthode lors de l'étude de trois systèmes suffisamment simples pour avoir accès aux résultats exacts, ont été comparés à ceux obtenus par d?autres méthodes mixtes déjà largement utilisées
Utilisation des "trajectoires quantiques" dans des processus dynamiques moléculaires
TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF
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