Small helium clusters formation

Abstract

We investigated small helium clusters formation in nonequilibrium conditions using the non‐Hermitian formalism. Helium is a simple enough system for analytical study while complicated enough to have a rich variety of quantum properties. In this article, we used a new formalism based on non‐Hermitian quantum mechanics for describing the electronic excited states in clusters. This formalism enabled to estimate the decay time of excited states within a single scheme. Its implementation to helium shows the existence of new long‐lived excited states in small helium clusters at the distance of 5.6 Bohr radii between atoms. Moreover, several helium excimers and exciplexes at the distances between helium atoms of 35.5, 22.8, 14.0, and 8.5 Bohr radii with the scaling factor of about 1.6 were found. It is related to the restructuring of the electronic structure caused by powerful external excitations. These results give a new insight on clustering processes providing more profound and complete understanding.

Modeling intermolecular Coulombic decay with non-Hermitian real-time time-dependent density functional theory

“…In general, the majority of theoretical analysis of such processes has relied on static electronic structure calculations involving analyzing the ionization spectrum, [6][7][8] density of states, 9 or the broadening of the electronic states through non-Hermitian techniques. [10][11][12] However, with the advent of attosecond spectroscopy, it is now possible to have experimentally time-resolved observation of ultra-fast processes with sub-femtosecond resolution. [13][14][15] Therefore, there is a benefit to develop practical simulation methods that go beyond static techniques and can more directly report on such experiments.…”

Modeling Intermolecular Coulombic Decay with Non-Hermitian Real-Time Time-Dependent Density Functional Theory

“…The ionization of an inner-valence or core electron can initiate competing electronic relaxation pathways that occur on an ultrafast time scale, such as Auger–Meitner, intermolecular Coulombic decay (ICD), and electron-transfer-mediated decay (ETMD) processes. − These processes play an important role in surface-science fragmentation and biological systems; , the initial electron dynamics governs the subsequent fragmentation product distribution due to the Coulomb explosion of charged species in close proximity. In general, the majority of theoretical investigation of such processes has relied on static electronic structure calculations involving analysis of the ionization spectrum, − density of states, or broadening of the electronic states through non-Hermitian techniques. − However, with the advent of attosecond spectroscopy, it is now possible to have experimentally time-resolved observation of ultrafast processes with subfemtosecond resolution. − Therefore, there is a benefit to developing practical simulation methods that go beyond static techniques and can more directly report on such experiments. Real-time electronic structure methods, which directly solve for the time propagation of the electronic wave function, provide a powerful class of techniques for accomplishing such a goal. − In the context of electronic relaxation dynamics, a few highly accurate real-time studies of the explicit electronic motion have been performed on small systems, such as using the wave packet propagation method to simulate ICD in the Ne–Ar system and the MCTDH method for Fermions to simulate ICD in model potentials of quantum dots. − Additionally, a few studies have used real-time time-dependent density functional theory (RT-TDDFT) with various levels of success. , …”