Non-adiabatic quantum molecular dynamics: basic formalism and case study

Saalmann, Ulf; Schmidt, R.

doi:10.1007/s004600050077

Cited by 101 publications

(92 citation statements)

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“…Correspondence to: skuemmel@tulane.edu par excellence, allowing to study metallic behavior in one of its purest forms, a lot of theoretical work over the years has been devoted to photoabsorption in Na clusters [5,6,7,8,9,10,11,12,13,14,15]. From these studies, two different and somewhat opposing points of view on the interpretation of the observed resonances emerged.…”

Section: Introductionmentioning

confidence: 99%

Collectivity in the optical response. of small metal clusters

Kümmel

Andrae

Reinhard

2001

Applied Physics B: Lasers and Optics

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The question whether the linear absorption spectra of metal clusters can be interpreted as density oscillations (collective "plasmons") or can only be understood as transitions between distinct molecular states is still a matter of debate for clusters with only a few electrons. We calculate the photoabsorption spectra of Na 2 and Na + 5 comparing two different methods: quantum fluid-dynamics and time-dependent density functional theory. The changes in the electronic structure associated with particular excitations are visualized in "snapshots" via transition densities. Our analysis shows that even for the smallest clusters, the observed excitations can be interpreted as intuitively understandable density oscillations. For Na + 5 , the importance of self-interaction corrections to the adiabatic local density approximation is demonstrated.

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Section: Introductionmentioning

confidence: 99%

Collectivity in the optical response. of small metal clusters

Kümmel

Andrae

Reinhard

2001

Applied Physics B: Lasers and Optics

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“…Recently, a general theory has been developed [27] which is able to describe simultaneously adiabatic and non-adiabatic collisions and, in particular, also the still completely unknown transition regime where both -electronic and vibrational -excitations occur. This so-called non-adiabatic quantum molecular dynamics (NA-QMD) [27] can also be used to study, for the first time, phase transitions in and fragmentation of clusters induced by electronvibration coupling.In this work, different excitation mechanisms (electronic and vibrational) as well as related relaxation phenomena (phase transitions and fragmentation) in cluster collisions are studied in the microscopic framework of NA-QMD. This theory treats electronic and vibrational degrees of freedom simultaneously and selfconsistently in atomic many-body systems by combining time-dependent density functional theory [28] with classical MD.…”

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confidence: 99%

“…On the other hand, electronic transitions in non-adiabatic cluster collisions have been treated with classical [22,23], semi-classical [24], or oneelectron quantum mechanical [25,26] approaches where the atomic structure, and thus the vibrational degrees of freedom, are not taken into account. Recently, a general theory has been developed [27] which is able to describe simultaneously adiabatic and non-adiabatic collisions and, in particular, also the still completely unknown transition regime where both -electronic and vibrational -excitations occur. This so-called non-adiabatic quantum molecular dynamics (NA-QMD) [27] can also be used to study, for the first time, phase transitions in and fragmentation of clusters induced by electronvibration coupling.…”

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Excitation and Relaxation in Atom-Cluster Collisions

Saalmann

Schmidt

1998

Phys. Rev. Lett.

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Electronic and vibrational degrees of freedom in atom-cluster collisions are treated simultaneously and self-consistently by combining time-dependent density functional theory with classical molecular dynamics. The gradual change of the excitation mechanisms (electronic and vibrational) as well as the related relaxation phenomena (phase transitions and fragmentation) are studied in a common framework as a function of the impact energy (eV. . . MeV). Cluster "transparency" characterized by practically undisturbed atom-cluster penetration is predicted to be an important reaction mechanism within a particular window of impact energies.PACS numbers: 31.70. Hq, 31.15.Ew, 34.50.Bw, 36.40.Ei Collisions with atomic clusters represent a relatively new branch of collision physics as compared to the well established fields of ion-atom collisions [1] and ion-solid interaction [2]. The study of cluster collisions is of particular interest and importance because it offers the possibility to tackle bridge-building questions (like the continuous transition from individual excitations in the elementary ion-atom collision to the macroscopic stopping power in solids) as well as fundamental problems (like phase transitions in finite systems). It is also an extremely challenging and complicated field as the comprehensive understanding of these collisions still requires the development of basically new techniques for both, large-scale (multi-parametric) experiment and manybody (quantum-mechanical) theory. In this request, the present situation resembles very much that of nuclear physics at the beginning of the 80's [3].Experimentally, large progress has been made, meanwhile, in the investigation of adiabatic cluster collisions where the reaction mechanism is determined by vibrational excitations only. Typical examples are the study of the vibrational energy transfer [4], the fusion between clusters [5], the formation of endohedral complexes [6], and the collision induced dissociation (CID) [7]. There is also a lasting interest to study non-adiabatic cluster collisions where electronic transitions occur. Experiments in this field concern the measurements of the charge transfer [8][9][10], ionization and electronic excitation [11], as well as the selective observation of vibrational and electronic excitations [12].Theoretically, adiabatic cluster collisions can be well described by quantum molecular dynamics (QMD) or molecular dynamics (MD) [13][14][15][16][17]. Also, isomeric [18] and solid-liquid phase transitions [19,20] [25,26] approaches where the atomic structure, and thus the vibrational degrees of freedom, are not taken into account. Recently, a general theory has been developed [27] which is able to describe simultaneously adiabatic and non-adiabatic collisions and, in particular, also the still completely unknown transition regime where both -electronic and vibrational -excitations occur. This so-called non-adiabatic quantum molecular dynamics (NA-QMD) [27] can also be used to study, for the first time, phase transitions i...

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“…For example, Ehrenfest MD (EMD) can also be one AIMD scheme if TDDFT is used to propagate the electronic subsystem. This is the most common manner in which TDDFT and MD have been combined in the past: as a means to study fast out-of-equilibrium processes, typically intense laser irradiations or ionic collisions [Saalmann 1996, Saalmann 1998, Reinhard 1999, Kunert 2001, Castro 2004.…”

Section: Introductionmentioning

confidence: 99%

On the Combination of TDDFT with Molecular Dynamics: New Developments

Alonso

Castro

Echenique

et al. 2012

Fundamentals of Time-Dependent Density Functional Theory

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In principle, we should not need the time-dependent extension of density-functional theory (TDDFT) for excitations, and in particular not for Molecular Dynamics (MD) studies: the theorem by Hohenberg and Kohn teaches us that for any observable that we wish to look at (including dynamical properties or observables dependent on excited states) there is a corresponding functional of the ground-state density. Yet the unavailability of such magic functionals in many cases (the theorem is a non-constructive existence result) demands the development and use of the alternative exact reformulation of quantum mechanics provided by TDDFT. This theory defines a convenient route to electronic excitations and to the dynamics of a many-electron system subject to an arbitrary time-dependent perturbation. This is, in fact, the main purpose of inscribing TDDFT in a MD framework -the inclusion of the effect of electronic excited states in the dynamics. However, as we will show in this review, it may not be the only use of TDDFT in this context. In this manuscript, we review two recent proposals: In Section 1.2, we show how TDDFT can be used to design efficient gsBOMD algorithms -even if the electronic excited states are in this case not relevant. The work described in Section 1.3 addresses the problem of mixed quantum-classical systems at thermal equilibrium.Comment: 10 pages, 1 figure, to be published in the book "Time Dependent Density Functional Theory" by Springer Verla

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Non-adiabatic quantum molecular dynamics: basic formalism and case study

Cited by 101 publications

References 31 publications

Collectivity in the optical response. of small metal clusters

Collectivity in the optical response. of small metal clusters

Excitation and Relaxation in Atom-Cluster Collisions

On the Combination of TDDFT with Molecular Dynamics: New Developments

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