Mixed Quantum-Classical Dynamics in the Adiabatic Representation To Simulate Molecules Driven by Strong Laser Pulses (original) (raw)
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Ab Initio Nonadiabatic Quantum Molecular Dynamics
Chemical Reviews
The Born-Oppenheimer approximation underlies much of chemical simulation and provides the framework defining the potential energy surfaces that are used for much of our pictorial understanding of chemical phenomena. However, this approximation breaks down when considering the dynamics of molecules in excited electronic states. Describing dynamics when the Born-Oppenheimer approximation breaks down requires a quantum mechanical description of the nuclei. Chemical reaction dynamics on excited electronic states is critical for many applications in renewable energy, chemical synthesis, and bioimaging. Furthermore, it is necessary in order to connect with many ultrafast pump-probe spectroscopic experiments. In this review, we provide an overview of methods that can describe nonadiabatic dynamics with emphasis on those that are able to simultaneously address the quantum mechanics of both electrons and nuclei. Such ab initio quantum molecular dynamics methods solve the electronic Schrödinger equation alongside the nuclear dynamics and thereby avoid the need for precalculation of potential energy surfaces and nonadiabatic coupling matrix elements. Two main families of methods are commonly employed to simulate nonadiabatic dynamics in molecules: full quantum dynamics such as the multiconfigurational time-dependent Hartree method and classical trajectory-based approaches such as trajectory surface hopping. In this review, we describe a third class of methods that is intermediate between the two-Gaussian basis set expansions built around trajectories.
Electron-nuclear dynamics with diabatic and adiabatic wave packets
The Journal of Physical Chemistry, 1988
reverse process of the chemical reactions of electrons with dipolar molecules. In a chemical reaction, an electron needs to get inside a centrifugal potential, while in photodetachment, the electron has to pass back out through the potential. The rotationally adiabatic theory is crucial in explaining both of these processes,34 and indeed, the photodetachment experiment explicitly probes these adiabatic potentials which control the chemical reaction rate. The same considerations are also true for the reactions and photodissociation of ions, although here many more adiabatic potentials are involved. It is clear that the rotationally adiabatic potentials are a very useful concept in understanding the chemistry of ions and electron-molecule interactions in the gas phase.
Journal of Chemical …
We present a semiclassical surface-hopping method which is able to treat arbitrary couplings in molecular systems including all degrees of freedom. A reformulation of the standard surface-hopping scheme in terms of a unitary transformation matrix allows for the description of interactions like spinÀorbit coupling or transitions induced by laser fields. The accuracy of our method is demonstrated in two systems. The first one, consisting of two model electronic states, validates the semiclassical approach in the presence of an electric field. In the second one, the dynamics in the IBr molecule in the presence of spinÀorbit coupling after laser excitation is investigated. Due to an avoided crossing that originates from spinÀorbit coupling, IBr dissociates into two channels: I þ Br( 2 P 3/2 ) and I þ Br*( 2 P 1/2 ). In both systems, the obtained results are in very good agreement with those calculated from exact quantum dynamical simulations.
Adiabatic Passage by Light-Induced Potentials in Molecules
Physical Review Letters, 1998
We present the APLIP process (Adiabatic Passage by Light Induced Potentials) for the adiabatic transfer of a wave packet from one molecular potential to the displaced ground vibrational state of another. The process uses an intermediate state, which is only slightly populated, and a counterintuitive sequence of light pulses to couple the three molecular states. APLIP shares many features with STIRAP (stimulated Raman adiabatic passage), such as high efficiency and insensitivity to pulse parameters. However, in APLIP there is no two-photon resonance, and the main mechanism for the transport of the wave packet is a light-induced potential. The APLIP process appears to violate the Franck-Condon principle, because of the displacement of the wave packet, but does in fact take place on timescales which are at least a little longer than a vibrational timescale.
Journal of Physical Chemistry A, 2001
The electronic excitation induced by ultrashort laser pulses and the subsequent photodissociation dynamics of molecular fluorine in an argon matrix are studied. The interactions of photofragments and host atoms are modeled using a diatomics-in-molecule Hamiltonian. Two types of methods are compared: (1) quantumclassical simulations where the nuclei are treated classically, with surface-hopping algorithms to describe either radiative or nonradiative transitions between different electronic states, and (2) fully quantum-mechanical simulations, but for a model system of reduced dimensionality, in which the two most essential degrees of freedom are considered. Some of the main results follow: (1) The sequential energy transfer events from the photoexcited F 2 into the lattice modes are such that the "reduced dimensionality" model is valid for the first 200 fs. This, in turn, allows us to use the quantum results to investigate the details of the excitation process with short laser pulses. Thus, it also serves as a reference for the quantum-classical "surface hopping" model of the excitation process. Moreover, it supports the validity of a laser pulse control strategy developed on the basis of the "reduced dimensionality" model. (2) In both the quantum and quantum-classical simulations, the separation of the F atoms following photodissociation does not exceed 20 bohr. The cage exit mechanisms appear qualitatively similar in the two sets of simulations, but quantum effects are quantitatively important.
Frontiers in Optics 2013, 2013
The nonadiabatically coupled dynamics of electrons and nuclei is investigated for the ozone molecule on the attosecond time scale. A coherent superposition of nuclear wave packets located on different electronic states in the Chappuis and in the Hartley bands are created by pump pulses. The multiconfiguration time-dependent Hartree method is used to solve the coupled nuclear quantum dynamics in the framework of the adiabatic separation of the time-dependent Schrödinger equation including nonadiabatic couplings. Our nuclear wave-packet calculations demonstrate that the coherence between Hartley state B and one of the Chappuis states (Chappuis 1) is significantly large, while it is almost negligible for the other two cases (between Hartley B and Chappuis 2 or between Chappuis 1 and Chappuis 2). At present we limited our description of the electronic motion to the Franck-Condon region only due to the localization of the nuclear wave packets around this point during the first 5-6 fs.
Attosecond-resolution quantum dynamics calculations for atoms and molecules in strong laser fields
Physical Review E, 2008
A parallel quantum electron and nuclei wave packet computer code, LZH-DICP, has been developed to study laser-atom-molecule interaction in the nonperturbative regime with attosecond resolution. The nonlinear phenomena occurring in that regime can be studied with the code in a rigorous way by numerically solving the time-dependent Schrödinger equation of electrons and nuclei. Time propagation of the wave functions is performed using a split-operator approach, and based on a sine discrete variable representation. Photoelectron spectra for hydrogen and kinetic-energy spectra for molecular hydrogen ion in linearly polarized laser fields are calculated using a flux operator scheme, which testifies to the validity and the high efficiency of LZH-DICP.
Mixed quantum-classical treatment of reactions at surfaces with electronic transitions
Israel Journal of Chemistry, 2005
The reliable high-dimensional theoretical description of reactions at surfaces with electronic transitions still represents a considerable challenge since the electrons have to be treated quantum mechanically. A full quantum treatment of both electrons and nuclei is computationally not feasible at the moment. Therefore we propose a mixed quantum-classical approach for the simulation of reactions at surfaces with electronic transitions. In this method, the nuclear motion is described classically while the electrons are treated quantum mechanically. Still the feedback between nuclei and electrons is taken into account self-consistently. The computational efficiency of this method allows a more realistic multi-dimensional treatment of electronically non-adiabatic processes at surfaces. We will discuss two recent applications of this approach. First we will address the charge transfer in the scattering of I2 from a diamond surface. As a second example we present dynamical simulations of the laser induced desorption of NO from NiO(100).
Molecular Dynamics in Strong Laser Fields
IEEE Journal of Selected Topics in Quantum Electronics, 2000
One of the goals for strong field physics is imaging the dynamics of the quantum systems, and in case of molecules, there is strong interest in imaging of the electron rearrangement during chemical reactions. Strong field ionization of molecules has many attractive features that make this process a candidate tool for strong field imaging of transient states and chemical reactions. In this paper, we present analysis of ionization dependence on orientation of molecular axis with respect to polarization of the electric field of the laser. By considering several examples of molecules at their equilibrium internuclear distances and an example of the simplest chemical reaction, namely, the dissociation of diatomic molecule, we present how symmetries of the molecular orbitals influence the alignment-dependent ionization and how this dependence can be used to follow molecular dynamics using strong field multiphoton ionization.