Bound electronic states of the smallest fullerene C20- anion.

We report on high-level coupled-cluster calculations for the anion states of the smallest fullerene C20. Using the state-of-the-art EA-EOM-CCSD method we revealed that the C20- anion has five bound electronic states at the C20 neutral ground-state D3d equilibrium configuration. These are two pairs of 2Eu and 2A2u states and one 2A1g state. The binding energies vary from 2.05 eV for the most bound 2Eu state to <1 meV for the 2A1g state. An analysis in terms of radial and angular density distribution of the excess electron revealed that the two 2Eu/2A2u pairs are valence-like states while 2A1g corresponds to a super-atomic-like (SAMO) state. The valence states of the first 2Eu/2A2u pair were found to be of p-type whereas those of the second pair are of hybrid sp-type. We have also applied a simple model to understand the binding of the excess electron in C20-. The model confirms the existence of only one SAMO state of the s-type for C20-. At the same time, it overestimates the number of the bound valence states of C20-.

How many bound valence states does the C60⁻ anion have?

We report on unprecedentedly large coupled cluster calculations for the C60(-) anion, and on a heuristic model uncovering the valence states of C60(-) that allow the resolution of the headlined question. Our results convincingly demonstrate that C60(-) possesses as many as four bound valence states: (2)T1u, (2)T1g, (2)T2u and (2)Hg. Our findings reconcile previous controversies regarding the existence of the bound (2)T2u and (2)Hg states. For all bound states of C60(-) we present an analysis of the radial and angular distributions of the excess electron, which reveals some unique properties of the valence states. Some interesting features of the introduced model are analyzed and discussed.

Barrierless Single-Electron-Induced cis-trans Isomerization.

Lowering the activation energy of a chemical reaction is an essential part in controlling chemical reactions. By attaching a single electron, a barrierless path for the cis-trans isomerization of maleonitrile on the anionic surface is formed. The anionic activation can be applied in both reaction directions, yielding the desired isomer. We identify the microscopic mechanism that leads to the formation of the barrierless route for the electron-induced isomerization. The generalization to other chemical reactions is discussed.

The best orbital and pair function for describing ionic and excited states on top of the exact ground state.

Many-body processes inevitably lead to the transition from one many-body wavefunction to another. Due to the complexity of the initial and final states many-body wavefunctions, one often wishes to try and describe such transitions using only a single-particle function. While there are numerous types of orbitals and densities which are commonly used, the question remains which one is optimal and in which sense. Here we present the optimal one and two body functions whose anti-symmetrized product with the initial state yields the maximal overlap with the final state. A definition of the above optimal condition and its rigorous proof are given. The resulting optimal functions shed additional light on the well-known Dyson orbital and reduced transition matrix, demonstrating further their physical meaning as independent functions.

Ionization satellites of the ArHe dimer.

Ionization satellites are key ingredients in the control of post ionization processes such as molecular dissociation and interatomic Coulombic decay. Here, using the high-level ab initio method of multi-reference configuration interaction up to triple excitations, we study the potential energy curves (PECs) of the ionization satellites of the ArHe dimer. With this model system, we demonstrate that the simple model used in alkaline earth metal and rare gas complexes to describe the satellites as a Rydberg electron moving on top of a dicationic core does not fully hold for the rare gas clusters. The more complex valence structure in the rare gas atom leads to the mixing of different electronic configurations of the dimer. This prevents one from assigning a single dicationic parent state to some of the ionization satellites. We further analyze the structure of the different PECs, demonstrating how the density of the Rydberg electron is reflected in the structure of the PEC wherever the simple model is applicable.

All for one and one for all: accommodating an extra electron in C60.

Much like the neutral C60 fullerene, the C60(-) anion possesses certain unique properties which have attracted a great deal of research. One of these special properties, only recently fully uncovered, is that the C60(-) anion supports a substantial number of electronically stable excited states in contrast to other molecular anions with comparable electron affinity. In this work, we clarify how the C60(-) anion can support so many stable states by analyzing the radial and angular distributions of the excess electron bound to the anion. The analysis is based on ab initio calculations which are by far the most accurate on the C60(-) anion to date. Surprisingly, the radial distributions are highly similar for states of very different binding energies and the analysis stresses the importance of angular correlation in binding the excess electron. We further analyze the effect of the single excess electron on the electrons of the underlying neutral molecule. We demonstrate how this substantially modifies the actual distribution of the excess charge by shifting the underlying electron density. Implications of these findings are discussed.

The exact wavefunction factorization of a vibronic coupling system.

We investigate the exact wavefunction as a single product of electronic and nuclear wavefunction for a model conical intersection system. Exact factorized spiky potentials and nodeless nuclear wavefunctions are found. The exact factorized potential preserves the symmetry breaking effect when the coupling mode is present. Additionally nodeless wavefunctions are found to be closely related to the adiabatic nuclear eigenfunctions. This phenomenon holds even for the regime where the non-adiabatic coupling is relevant, and sheds light on the relation between the exact wavefunction factorization and the adiabatic approximation.

Resonance theory for discrete models: methodology and isolated resonances.

We here consider open quantum systems defined on discretized space, motivated by experimental and theoretical interest in the electronic conduction through nanoscale devices such as molecular junctions and quantum dots. We particularly focus on effects of resonances on the conductance through the systems. We develop a method of calculating the conductance with the use of Green's function expansion with respect to the eigenstates of the effective Hamiltonian for the open quantum systems. Unlike previous methodologies where one can treat only narrow resonances far from the band edges in a satisfactory manner with a Lorentzian profile, our method provides a novel resonance profile which can be used to describe any isolated resonance in the spectrum even close to the band edges.

Suppression of photoionization by a static field.

The dc field Stark effect is studied theoretically for atoms in high intensity laser fields. We prove that the first-order perturbation corrections for the energy and photoionization rate vanish when the dc field strength serves as a perturbational strength parameter. Our calculations show that by applying a dc field in the same direction as the polarization direction of the ac field, the photoinduced ionization rate is almost entirely suppressed. This suppression is attributed to changes in the phase shift of the continuum atomic wave functions which can be controlled by the dc field.

Visualization of branch points in PT-symmetric waveguides.

The visualization of an exceptional point in a PT-symmetric directional coupler (DC) is demonstrated. In such a system the exceptional point can be probed by varying only a single parameter. Using the Rayleigh-Schrödinger perturbation theory we prove that the spectrum of a PT-symmetric Hamiltonian is real as long as the radius of convergence has not been reached. We also show how one can use a PT-symmetric directional coupler to measure the radius of convergence for non-PT-symmetric structures. For such systems the physical meaning of the rather mathematical term radius of convergence is exemplified.