Exploring the importance of quantum effects in nucleation: The archetypical Nen case

Abstract

The effect of quantum mechanics (QM) on the details of the nucleation process is explored employing Ne clusters as test cases due to their semi-quantal nature. In particular, we investigate the impact of quantum mechanics on both condensation and dissociation rates in the framework of the microcanonical ensemble. Using both classical trajectories and two semi-quantal approaches (zero point averaged dynamics, ZPAD, and Gaussian-based time dependent Hartree, G-TDH) to model cluster and collision dynamics, we simulate the dissociation and monomer capture for Ne(8) as a function of the cluster internal energy, impact parameter and collision speed. The results for the capture probability P(s)(b) as a function of the impact parameter suggest that classical trajectories always underestimate capture probabilities with respect to ZPAD, albeit at most by 15%-20% in the cases we studied. They also do so in some important situations when using G-TDH. More interestingly, dissociation rates k(diss) are grossly overestimated by classical mechanics, at least by one order of magnitude. We interpret both behaviours as mainly due to the reduced amount of kinetic energy available to a quantum cluster for a chosen total internal energy. We also find that the decrease in monomer dissociation energy due to zero point energy effects plays a key role in defining dissociation rates. In fact, semi-quantal and classical results for k(diss) seem to follow a common "corresponding states" behaviour when the proper definition of internal and dissociation energies are used in a transition state model estimation of the evaporation rate constants.

Quest for Inexpensive Hydrogen Isotopic Fractionation: Do We Need 2D Quantum Confining in Porous Materials or Are Rough Surfaces Enough? The Case of Ammonia Nanoclusters

“…[20][21][22]25 Here, we specifically consider extending a recently proposed Gaussianbased time dependent Hartree dynamics. 75 A "vis-a-vis"…”

“…Possible differences in aggregate structures due to the inclusion of quantum effects with, e.g., ring polymer molecular dynamics seem also worth investigating. With such models made available, it would be then possible to directly investigate adsorption isotherms and isotopic separation performances at finite T and p , as well as possible contributions to quantum sieving due to dynamic effects. − , Here, we specifically consider extending a recently proposed Gaussian-based time dependent Hartree dynamics . A “vis-à-vis” comparison with similar data obtained with water ice would also help to foster a better understanding of all variable that play a role in these complicate phenomena.…”

Nuclear Quantum Effects in H2 Adsorption Dynamics on a Small Water Cluster Studied with Ring-Polymer Molecular Dynamics Simulations

“…They have concluded that the reduction of the cross section comes from the reduction in the effective interaction owing to quantized vibrational zero-point effects. The importance of the quantized vibrational energy has also been pointed out in the study by Unn-Toc et al on the condensation and dissociation dynamics processes in Ne clusters …”

Vibrationally Inelastic Collision Between Li2(ν = 0) and Li: Direct and Postponed Elongation Mechanisms

“…Trajectory initial conditions imposed to Li 2 a vibrational energy equal to its vibrational ground state ( E 0 = 0.476 kcal/mol) and an angular momentum J = 0 via the efficient microcanonical sampling approach − used previously. − Four different collision energies ( 1.69, 3.62, 6.27, and 9.64 kcal/mol) were used to explore the dependency of the excitation cross section (σ­(0 → ν′)) on the projectile speed ( v p ). Twenty-one impact parameters (0 ≥ b ≥ 20 bohr) were used to compute the opacity function P ( b , v p ,0 → ν′) needed to obtain the process cross section; 20 000 trajectories were launched for each b value with an initial atom–diatom distance of 40 bohr.…”