Quantum dynamics simulations of nonadiabatic processes in many-atom systems: Photoexcited Ba(Ar)10 and Ba(Ar)20 clusters

Abstract

Semiclassical molecular dynamics simulations of lowtemperature clusters: Applications to (Ar)13; (Ne)13; (H2O) n , n=2,3,5Quantum simulations are reported for the dynamics following the photoexcitation Ba͑ 1 S͒→Ba͑ 1 P͒ in Ba͑Ar͒ 10 and Ba͑Ar͒ 20 clusters. The evolution in time is studied in a framework that treats quantum-mechanically all the coupled degrees of freedom. The focus is on the role of nonadiabatic transitions between the three adiabatic surfaces corresponding to the P states of the Ba atom. The time scales of electronic relaxation and of electronic depolarization ͑orbital reorientation͒ are computed, and the competition between adiabatic and nonadiabatic effects is assessed. The calculations are carried out by a new scheme that extends the recent classically based separable potential method. Semiclassical surface-hopping simulations are used to produce effective single-mode potentials on which nuclear ''orbitals'' are then generated. The full wave packet is constructed from the electronic states involved, and from these nuclear wave functions. Among the main results we find that nonadiabatic transitions become appreciable around 1 ps after photoexcitation, and they are stronger in the smaller cluster. Comparing Tully's semiclassical method with the quantum simulations, good qualitative agreement is found. Quantitatively, the semiclassical predictions for the electronic states branching rations deviate from the quantum results roughly by a factor of 2 after 1 ps. In the smaller cluster direct dissociation of the Ba atom dominates over energy redistribution within the cluster, the opposite being true for the large system. This example demonstrates the feasibility of quantum simulations of nonadiabatic processes in large systems with the new method.

Many-body effects on the structures and stability of Ba2+Xen (n = 1–39, 54) clusters

“…One possible extension suggested by some of the above analyses could be devoted to the characterization of those clusters at finite temperature, evaluating, for instance, their relative stability based on free energies. 50 It would also be interesting to compare the structural trends observed here to those of the related systems Ba + Xe n , and in case of significant differences study molecular processes such as post-ionization relaxation on the ground or electronic excited states, 19,35,37 especially in the case of Rydberg states. [51][52][53] …”

“…35,37 However, because dynamical properties often arise due to specific geometric arrangements it is essential to determine and understand the stable structures adopted by those clusters. Ab initio calculations [27][28][29][30][31][32][33] and empirical potentials 13,[19][20][21][22][23][24][25][26] have provided a lot of insight into measured magic numbers by highlighting the dominant contributions to bonding and connecting those contributions to geometric features such as high-symmetry shell completion.…”

Accurate quantum calculations of thermal rate constants employing MCTDH: H2+OH→H+H2O and D2+OH→D+DOH

“…Hartree calculations including 30 to 60 coordinates have been published. 36,37 The present approach avoids the use of negative imaginary ͑absorbing͒ potentials or similar tools. This considerably simplifies the practical computation.…”

Dynamics of highly excited barium atoms deposited on large argon clusters. I. General trends

“…Theoretical approaches examined the photoinduced dynamics of these systems. 12,22,23 Other theoretical works examined more complex situations where a diatomic molecule is photoexcited on or embedded in argon clusters. In the latter case, a diversity of processes was examined such as dissociation, 24,25 recombination, 24,26,27 and spin nonconserving transitions, 24 and information was given on the factors influencing them such as size and local environment.…”