Stability of small positronic atoms in ground and excited states

Studying the dynamical stability of positron-atom and positron-molecule complexes provides an insight into the physics and chemistry of low energy positrons and their interaction with matter. Beams of low energy positrons have applications in medical imaging (positron emission tomography) and materials science (positron annihilation spectroscopy). The first theoretical confirmation of the stability of a positronic atom (e+Li) was obtained back in 1997 [1]. However, many facts remain undiscovered. In particular, this concerns the existence of excited states

Quantum dynamics in molecules and nanostructures in strong fields

With the advance of time-dependent probes the investigation of the dynamical behavior of matter at the nanoscale has become a very important research direction. Laser-assisted steering of the electron motion in molecules and manipulation of their structure and composition has been dreamt about since the very emergence of coherent light sources. Realizing new possibilities in selective photochemistry of complex molecular systems, however, requires good understanding of underlying quantum dynamics. First-principles quantum-mechanical simulations can be of great help in assisting experiments, understanding the complex quantum dynamics, and interpreting the experimental data

Quantum dynamics in molecules and nanostructures in strong fields

With the advance of time-dependent probes the investigation of the dynamical behavior of matter at the nanoscale has become a very important research direction. Laser-assisted steering of the electron motion in molecules and manipulation of their structure and composition has been dreamt about since the very emergence of coherent light sources. Realizing new possibilities in selective photochemistry of complex molecular systems, however, requires good understanding of underlying quantum dynamics. First-principles quantum-mechanical simulations can be of great help in assisting experiments, understanding the complex quantum dynamics, and interpreting the experimental data

Enhanced ionization of acetylene in intense laser pulses is due to energy upshift and field coupling of multiple orbitals

Synopsis We describe a new enhanced ionization mechanism for polyatomic molecules. It works via a significant energy up-shift of valence orbitals for stretched bonds and a strong concomitant increase in the coupling between multiple molecular orbitals

Controllable functionalization and wettability transition of graphene-based films by an atomic oxygen strategy

Though chemical modification of graphene based on Hummers method has been most widely used to tailor its properties and interfacial characteristics, a method which could achieve definitive and controllable groups and properties is still highly required. Here, we demonstrate a high-vacuum oxidation strategy by atomic oxygen (AO) and investigate the AO induced functionalization and wettability transition in films made from basal-defect- and oxide-free graphene dispersions. These graphene-based films are neither graphene nor graphite, but graphene blocks constituted by numerous randomly stacked graphene flakes. It is found that AO induced functionalization of these films through the formation of epoxy groups, sp(3) configuration, ether, and double and triple C–O groups. The films turn to be hydrophilic after exposed to AO. The contact angle increases with AO exposure time. This phenomenon is attributed to the lower surface roughness induced by collision and/or edge erosion of energetic ions to the film surface and is further explained by the Wenzel model. The demonstrated strategy can overcome limitations of Hummers method, provide possibility to gain functionalization and wettability transition in liquid-phase exfoliated basal-defect- and oxide-free graphene in the dry environment, and may extend the study and application of this material in spacecraft in low earth orbit

Low-lying S 2 states of the singly charged carbon ion

In this work, we report benchmark variational calculations of the five lowest doublet S-states of the C+ ion. The wave functions of this five-electron system are expanded in terms of 16 000 all-particle explicitly correlated Gaussians (ECGs) whose nonlinear variational parameters are subject to extensive optimization. The motion of the finite-mass nucleus is explicitly included in the Hamiltonian, while relativistic corrections to the energy levels are computed in the framework of the perturbation theory. Lowest-order quantum electrodynamics (QED) corrections are also estimated. The results obtained for the energy levels enable the determination of transition frequencies with the accuracy that approaches the available experimental data and may open up avenues for future determination of nuclear charge radii of carbon isotopes. © 2020 American Physical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Matrix elements of N-particle explicitly correlated Gaussian basis functions with complex exponential parameters

In this work we present analytical expressions for Hamiltonian matrix elements with spherically symmetric, explicitly correlated Gaussian basis functions with complex exponential parameters for an arbitrary number of particles. The expressions are derived using the formalism of matrix differential calculus. In addition, we present expressions for the energy gradient that includes derivatives of the Hamiltonian integrals with respect to the exponential parameters. The gradient is used in the variational optimization of the parameters. All the expressions are presented in the matrix form suitable for both numerical implementation and theoretical analysis. The energy and gradient formulas have been programed and used to calculate ground and excited states of the He atom using an approach that does not involve the Born-Oppenheimer approximatio

S 2 Rydberg spectrum of the boron atom

Benchmark variational calculations of the lowest ten Rydberg S2 states of two stable isotopes of the boron atom (B10 and B11) are reported. The nonrelativistic wave functions of this five-electron system are expanded in terms of 16 000 all-particle explicitly correlated Gaussians (ECGs). The ECG nonlinear exponential parameters are extensively optimized using a procedure that employs the analytic gradient of the energy with respect to these parameters. A finite nuclear mass value is used in the calculations and the motion of the nucleus is explicitly represented in the nonrelativistic Hamiltonian. The leading relativistic corrections to the energy levels are computed in the framework of the perturbation theory. The lowest-order quantum electrodynamics corrections are also estimated. The results obtained for the energy levels enable determination of interstate transition frequencies with accuracy that approaches the available experimental spectroscopic data. © 2021 American Physical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]