Simulations of Nano-Structures in Time Dependent External Fields (original) (raw)
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Strong laser-pulse-driven ionization and Coulomb explosion of hydrocarbon molecules
Physical Review A, 2012
Field ionization and Coulomb explosion of small hydrocarbon molecules driven by intense laser pulses are studied in a combined theoretical and experimental framework. The spectra of ejected protons calculated by the time-dependent density functional approach are in good agreement with the experimental data. The results of the simulations give detailed insight into the correlated electron and nuclear dynamics and complement the experiment with a time-dependent physical picture. It is demonstrated that the Coulomb explosion in the studied molecular systems is a sudden, all-at-once fragmentation where the ionization step is followed by a simultaneous ejection of the charged fragments.
Excited states dynamics in time-dependent density functional theory
The European Physical Journal D - Atomic, Molecular and Optical Physics, 2004
We present a theoretical description of femtosecond laser induced dynamics of the hydrogen molecule and of singly ionised sodium dimers, based on a real-space, real-time, implementation of time-dependent density functional theory (TDDFT). High harmonic generation, Coulomb explosion and laser induced photo-dissociation are observed. The scheme also describes non-adiabatic effects, such as the appearance of even harmonics for homopolar but isotopically asymmetric dimers, even if the ions were treated classically. This TDDFT-based method is reliable, scalable, and extensible to other phenomena such as photoisomerization, molecular transport and chemical reactivity.
Time-dependent density-functional studies of the D2 coulomb explosion
The journal of physical chemistry. A, 2006
Real-time first principle simulations are presented of the D(2) Coulomb explosion dynamics detonated by exposure to very intense few-cycle laser pulse. Three approximate functionals within the time-dependent density functional theory (TDDFT) functionals are examined for describing the electron dynamics, including time-dependent Hartree-Fock theory. Nuclei are treated classically with quantum corrections. The calculated results are sensitive to the underlying electronic structure theory, showing too narrow kinetic energy distribution peaked at too high kinetic energy when compared with recent experimental results (Phys. Rev. Lett. 2003, 91, 093002). Experiment also shows a low energy peak which is not seen in the present calculation. We conclude that while Ehrenfest-adiabatic-TDDFT can qualitatively account for the dynamics, it requires further development, probably beyond the adiabatic approximation, to be quantitative.
Physics Reports, 2015
There are various ways to analyze the dynamical response of clusters and molecules to electromagnetic perturbations. Particularly rich information can be obtained from measuring the properties of electrons emitted in the course of the excitation dynamics. Such an analysis of electron signals covers observables such as total ionization, Photo-Electron Spectra (PES), Photoelectron Angular Distributions (PAD), and ideally combined PES/PAD. It has a long history in molecular physics and was increasingly used in cluster physics as well. Recent progress in the design of new light sources (high intensity, high frequency, ultra short pulses) opens new possibilities for measurements and thus has renewed the interest on these observables, especially for the analysis of various dynamical scenarios, well beyond a simple access to electronic density of states. This, in turn, has motivated many theoretical investigations of the dynamics of electronic emission for molecules and clusters up to such a complex and interesting system as C60. A theoretical tool of choice is here Time-Dependent Density Functional Theory (TDDFT) propagated in real time and on a spatial grid, and augmented by a Self-Interaction Correction (SIC). This provides a pertinent, robust, and efficient description of electronic emission including the detailed pattern of PES and PAD. A direct comparison between experiments and well founded elaborate microscopic theories is thus readily possible, at variance with more demanding observables such as for example fragmentation or dissociation cross sections.
Chemical reaction dynamics studies emerged with the advent of quantum mechanical theories in 1920s which have the capability of predicting the atomic motions by calculating potential energy surfaces. Experimental studies in this field began to flourish with the advances in molecular beam generation and laser beam technologies many years later leading to the Nobel prize awarded to Herschbach, Lee, and Polanyi in 1986. Later in 1980s, advances in the production of frequency tunable ultrashort laser pulses with the temporal resolution of femtoseconds led to the birth of the field of femto-chemistry which is the study of molecular dynamics in real time. In the last few decades, various spectroscopic techniques exploiting ultrashort laser pulses have been developed to study the non-adiabatic dynamics of molecules in real time and space. Laser-induced Coulomb Explosion Imaging (CEI) is a powerful probe technique now emerging in this field, to unravel the structural changes of molecular sy...
Laser Coulomb-explosion imaging of small molecules
Physical Review A, 2005
We use intense few-cycle laser pulses to ionize molecules to the point of Coulomb explosion. We use Coulomb's law or ab initio potentials to reconstruct the molecular structure of D 2 O and SO 2 from the correlated momenta of exploded fragments. For D 2 O, a light and fast system, we observed about 0.3 Å and 15°d eviation from the known bond length and bond angle. By simulating the Coulomb explosion for equilibrium geometry, we showed that this deviation is mainly caused by ion motion during ionization. Measuring threedimensional structure with half bond length resolution is sufficient to observe large-scale rearrangements of small molecules such as isomerization processes.
Optical Properties of Nanostructures from Time-Dependent Density Functional Theory
Journal of Computational and Theoretical Nanoscience, 2004
We review the time-dependent density functional theory (TDDFT) and its use to investigate excited states of nanostructures. These excited states are routinely probed using electromagnetic fields. In this case, two different regimes are usually distinguished: (i) If the electromagnetic field is "weak"as in optical absorption of light-it is sufficient to treat the field within linear response theory; (ii) Otherwise, nonlinear effects are important, and one has to resort to the full solution of the timedependent Kohn-Sham equations. This latter regime is of paramount relevance in the emerging field of research with intense and ultrashort laser pulses. This review is divided into two parts: First we give a brief overview of the theoretical foundations of the theory, both in the linear and non-linear regimes, with special emphasis on the problem of the choice of the exchange-correlation functional. Then we present a sample of applications of TDDFT to systems ranging from atoms to clusters and to large biomolecules. Although most of these applications are in the linear regime, we show a few examples of non-linear phenomena, such as the photo-induced dissociation of molecules. Many of these applications have been performed with the recently developed code octopus (http://www.tddft.org/programs/octopus).
1998
Coulomb explosion of molecules induced by an intense femtosecond probe laser pulse provides an approach to measure structure and dynamics of internuclear wave packets on a natural spatial ͑Å͒ and temporal ͑fs͒ scale for molecules. The technique is illustrated by applying it to study photodissociation of I 2 initiated by a femtosecond pump pulse. We report a resolution of ϳ2-4 Å in the internuclear range ϳ7-14 Å using an 80-fs probe pulse. We discuss the ultimate spatial and temporal resolution of the technique, as well as the possibilities of observing dynamics of dissociating polyatomic molecules. Intense femtosecond laser pulses not only provide a way of probing molecular dynamics but they are also an efficient means to initiate dynamics in, e.g., molecular ionic states. ͓S1050-2947͑98͒10106-3͔