J. Zobeley

Ultrafast charge migration by electron correlation

Abstract Ultrafast charge migration in polyatomic systems driven solely by electron correlation is discussed and demonstrated. An explicit example is presented using large-scale ab initio Greens function calculations. It is expected that this mechanism is active in many systems.

Electronic decay in weakly bound heteroclusters: Energy transfer versus electron transfer

Inner-valence ionized states of weakly bound systems like van der Waals clusters can efficiently decay by electron emission. The mechanism of the decay, which does not occur in the isolated monomer units constituting the clusters has recently been shown to be of intermolecular/interatomic nature. This intermolecular/interatomic Coulombic decay (ICD) mechanism prevails in many systems ranging from hydrogen-bonded molecular clusters to atomic rare gas clusters. In the present paper we extend our previous studies to weakly bound heteroclusters built up of monomer units of largely differing energetics. It is shown that, as soon as the double ionization potential of a monomer unit is lower in energy than the ionization potential of the initially created inner-valence vacancy on a neighboring monomer unit, an additional electronic decay process can take place. In contrast to the ICD mechanism, which involves an efficient energy transfer between the monomer units, this second process is essentially based on an e...

Highly excited electronic states of molecular clusters and their decay

Highly excited electronic states of molecular clusters with intermediate-shell vacancies are calculated and analyzed using large scale ab initio Green’s function calculations. In sharp contrast to molecules, an intermolecular Coulombic mechanism has been found to lead to an ultrafast decay of singly and doubly ionized states with vacancies in the inner-valence region. Small hydrogen-bonded (HF)n clusters (n=2–4) have been selected as explicit examples to illustrate the proposed decay process, which does not occur in the HF monomer. The decay mechanism and the main factors that exercise an influence on it are discussed. The corresponding decay widths are estimated in selected cases, showing that the lifetimes of the states are of the order of few femtoseconds.

On the interatomic Coulombic decay in the Ne dimer

The interatomic Coulombic decay (ICD) in the Ne dimer is discussed in view of the recent experimental results. The ICD electron spectrum and the kinetic energy release of the Ne+ fragments resulting after Coulomb explosion of Ne2 (2+) are computed and compared to the measured ones. A very good agreement is found, confirming the dynamics predicted for this decay mechanism. The effect of the temperature on the electron spectrum is briefly investigated.

Fingerprints of the nodal structure of autoionizing vibrational wave functions in clusters: Interatomic Coulombic decay in Ne dimer

The removal of an inner-valence electron from neutral neon clusters leads to autoionization and subsequent fragmentation of the cationic clusters in accordance with the interatomic Coulombic decay mechanism discovered recently. Using non-Hermitian quantum scattering theory we investigate this process in detail for the Ne dimer. We show that a pronounced structure can be observed when measuring the autoionizing electron or the Ne+ kinetic energy distributions. This phenomenon is associated with the properties of the vibrational autoionizing resonance states of the electronically excited cationic dimer. By suppressing coherence among the different vibrational autoionizing resonances, or by selectively exciting one of them, the structures in the kinetic energy distributions become more pronounced. It is demonstrated that these structures reflect the nodal structure of the wave functions of the autoionizing vibrational states most populated by the initial ionization of the neutral neon dimer. In a coherent de...

Interatomic Coulombic decay in a heteroatomic rare gas cluster

Interatomic decay in a heteroatomic rare gas cluster (NeAr) is studied in detail using ab initio electronic structure description and nuclear dynamics simulations. Decay widths of all possible interatomic decay processes are calculated by the recently developed method based on Greens function formalism. Kinetic energy spectra of the electrons emitted in the course of interatomic Coulombic decay (ICD) are simulated for a series of initial vibrational states of the neutral cluster. The effect of the nuclear dynamics on the ICD electron spectra is discussed.

Intermolecular Coulombic decay of clusters

Abstract Following inner-valence ionization of a cluster, the system can relax by ultrafast electron emission. In contrast to Auger decay this novel process is intermolecular. It is characterized by an efficient Coulombic energy transfer mechanism between monomers in the cluster. As an example, we present an analysis of the hydrogen fluoride trimer, based on extensive ab initio computations.

Parallel filter diagonalization: A novel method to resolve quantum states in dense spectral regions

A parallel version of D. Neuhauser’s filter diagonalization algorithm is presented. In contrast to the usual procedure of acting with a set of narrow filter operators on a single or just a few initial vectors, parallelizability is achieved by working with a single, broad filter operator and a correspondingly large number of initial vectors. Apart from the obvious speedup in computation time, there is no need for communication between the processors involved in the computation. Furthermore, because a significantly reduced number of matrix vector multiplications is needed per initial vector, parallel filter diagonalization is numerically more stable than the single processor approach. It is argued that this method is particularly attractive for calculating eigenvectors of the large-scale secular matrices arising in quantum chemistry, especially in dense spectral regions. An application to dense state distributions of a cationic molecular cluster serves as an illustrative example. This is the first time filt...

Inner-valence ionization of molecular anions and ultrafast relaxation by electron emission

Relaxation mechanisms following inner-valence ionization of CN− are investigated using ab initio quantum chemistry methods. Due to a severe failure of the molecular orbital picture, there is a relatively large number of electronic states that are excited by ionization in the inner-valence regime. Most of these states are found to decay by electron emission, resulting in the formation of vibrationally bound CN+. General conclusions can be drawn concerning larger molecular anions.

Comparison of electronic decay of valence ionized fluorinated carbanions and their acids

The ionization and double-ionization spectra of fluorinated carbanions of various chain lengths are compared with those of their corresponding acids. For the acidic systems we find a dramatic relative shift of the double-ionization spectra to higher energies due to the presence of just one additional proton. The impact of the proton on the ionization spectra is also important, but results in only half of the double-ionization spectra’s shift. A molecular electronic decay mechanism is found to be operative in the valence region of the molecules under investigation. The impact of this decay is more substantial for the anions. The threshold for electronic decay (i.e., the first double-ionization potential) is at much lower energy for the anions than for the acids. Interestingly, the localization pattern of the holes in the decay channels is, in contrast to the decay threshold, only a little affected by protonation. We also compare the impact of electron correlation effects on the ionization and double-ioniza...