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Ab initio insights into plasmonic and strong-field contributions to H$_2$ dissociation on silver nanoshells

Natalia E. Koval, J. Iñaki Juaristi, Maite Alducin

TL;DR

The paper addresses how plasmonic excitation versus strong-field effects govern H$_2$ dissociation on a sizeable Ag nanoshell. By combining geometry optimization, real-time TDDFT, and Ehrenfest dynamics, it demonstrates that plasmons can dominate dissociation at resonant excitation ($ obreak obreak = obreak obreak$) and accelerate dissociation even at high intensities, while off-resonant, strong-field pathways can independently drive dissociation under certain conditions. The results identify pulse conditions and nanoshell size that allow disentangling plasmonic contributions from nonlinear effects, bridging the intensity gap between simulations and experiments. This work provides a framework to interpret plasmon-driven photochemistry under realistic TDDFT timescales and suggests directions to reach experimentally relevant regimes by scaling nanoparticle size and tuning pulse parameters.

Abstract

Modeling plasmonic catalysis by applying femtosecond laser pulses of high intensity ($10^{13}-10^{15}$ W cm$^{-2}$), although justified by the time-dependent density functional theory (TDDFT) time-scale limitations, can lead to a dissociation mechanism that is completely unrelated to the plasmon excitation created under low-intensity continuous light in experiments (on the order of 1 W cm$^{-2}$). In this study, we examine the dissociation of H$_2$ on a large octahedral Ag nanoshell under varying field intensity, frequency, and duration, and we explore the possibility of identifying optimal modeling conditions accessible with current TDDFT simulations. We show that using this large nanoshell that consists in the outer layer of the Ag$_{231}$ cluster, it is still possible to disentangle the role of the plasmon from strong-field effects at applied field intensities as high as $(2-8) \times 10^{13}$ W cm$^{-2}$. In particular, although strong-field effects are always present at these intensities, we find that the excited plasmon dominates the dissociation process at the lowest applied intensity of $2 \times 10^{13}$ W cm$^{-2}$. Furthermore, at the highest intensity, at which strong-field effects become dominant, the plasmon contributes to accelerating the dissociation of the molecule. Overall, our simulations pave the way to bridge the intensity gap between TDDFT modeling and experiments in plasmonic catalysis.

Ab initio insights into plasmonic and strong-field contributions to H$_2$ dissociation on silver nanoshells

TL;DR

The paper addresses how plasmonic excitation versus strong-field effects govern H dissociation on a sizeable Ag nanoshell. By combining geometry optimization, real-time TDDFT, and Ehrenfest dynamics, it demonstrates that plasmons can dominate dissociation at resonant excitation () and accelerate dissociation even at high intensities, while off-resonant, strong-field pathways can independently drive dissociation under certain conditions. The results identify pulse conditions and nanoshell size that allow disentangling plasmonic contributions from nonlinear effects, bridging the intensity gap between simulations and experiments. This work provides a framework to interpret plasmon-driven photochemistry under realistic TDDFT timescales and suggests directions to reach experimentally relevant regimes by scaling nanoparticle size and tuning pulse parameters.

Abstract

Modeling plasmonic catalysis by applying femtosecond laser pulses of high intensity ( W cm), although justified by the time-dependent density functional theory (TDDFT) time-scale limitations, can lead to a dissociation mechanism that is completely unrelated to the plasmon excitation created under low-intensity continuous light in experiments (on the order of 1 W cm). In this study, we examine the dissociation of H on a large octahedral Ag nanoshell under varying field intensity, frequency, and duration, and we explore the possibility of identifying optimal modeling conditions accessible with current TDDFT simulations. We show that using this large nanoshell that consists in the outer layer of the Ag cluster, it is still possible to disentangle the role of the plasmon from strong-field effects at applied field intensities as high as W cm. In particular, although strong-field effects are always present at these intensities, we find that the excited plasmon dominates the dissociation process at the lowest applied intensity of W cm. Furthermore, at the highest intensity, at which strong-field effects become dominant, the plasmon contributes to accelerating the dissociation of the molecule. Overall, our simulations pave the way to bridge the intensity gap between TDDFT modeling and experiments in plasmonic catalysis.

Paper Structure

This paper contains 7 sections, 1 equation, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Computational methodology
  3. Geometry optimization
  4. Real-time time-dependent density functional theory calculations of the absorption spectrum
  5. Ehrenfest molecular dynamics simulations
  6. Results and Discussion
  7. Conclusions and outlook

Figures (7)

  • Figure 1: (a) Relaxed structure of the Ag$_{231}^{\mathrm{L1}}$ nanoshell with H$_2$ (light pink spheres) adsorbed at 2.275 Å from the vertex (red sphere) surrounded by a layer of 258 ghost Ag atoms (small gray spheres). To facilitate visualization, green and blue spheres depict the nanoshell edge and facet Ag atoms, respectively. (b) Absorption spectrum of Ag$_{231}^{\mathrm{L1}}$+H$_2$ calculated with RT-TDDFT, showing the plasmon resonance at $\hbar \omega_{\mathrm{p}} = 2.48$ eV.
  • Figure 2: (a) Transient dipole moment $\mu(t)$ of the Ag$_{231}^{\mathrm{L1}}$+H$_2$ system induced by the Gaussian external field denoted pulse-1 in Table \ref{['table:pulses']} with a frequency of 2.48 eV (resonant, cyan curve) and 8 eV (off-resonant, orange curve). Corresponding Ag$_{231}^{\mathrm{L1}}$+H$_2$ induced density created at time $t = 10$ fs (i.e., near the induced dipole moment maxima) by (b) the resonant pulse-1 (isosurface value 0.00027588 e$^-$ bohr$^{-3}$) and (c) the off-resonant pulse-1 (isosurface value 0.000148458 e$^-$ bohr$^{-3}$). Vertical dashed line marks the instant $t_0 = 18$ fs of the pulse maximum.
  • Figure 3: (a) H$_2$ bond length and (b) and (c) Mulliken population change $\left[\Delta N_e = N_e(t)-N_e(t=0)\right]$ on H$_2$ and Ag$_{231}^{\mathrm{L1}}$, respectively, as a function of time. Results obtained from TDDFT-ED simulations of H$_2$ adsorbed on Ag$_{231}^{\mathrm{L1}}$ using as external field, pulse-1 (see Table \ref{['table:pulses']}) at resonant (2.48 eV, cyan solid lines) and off-resonant (8 eV, orange dashed lines) frequencies. For comparison, the results obtained for a gas-phase H$_2$ when applying the resonant pulse-1 are also shown by magenta dotted lines in (a) and (b). Vertical dashed line marks the instant $t_0 = 18$ fs of the pulse maximum.
  • Figure 4: (a) Time evolution of the H-H internuclear distance and (b) Mulliken population change $\left[\Delta N_e = N_e(t)-N_e(t=0)\right]$ on H$_2$. Results obtained from TDDFT-ED simulations for Ag$_{231}^{\mathrm{L1}}+$H$_2$ using pulse-1 (cyan), pulse-2 (magenta), and pulse-3 (orange) as resonant (2.48 eV) external fields (see Table \ref{['table:pulses']} for pulse details). Peak intensity instants $t_0$ are marked by vertical dashed lines following the same color code.
  • Figure 5: (a) H-H internuclear distance and (b) Mulliken population change $\left[\Delta N_e = N_e(t)-N_e(t=0)\right]$ on H$_2$ as a function of time for pulse-2 and pulse-4 (see pulses details in Table \ref{['table:pulses']}) at resonant (2.48 eV) and off-resonant (8 eV) field frequency. Results obtained from TDDFT-ED simulations for Ag$_{231}^{\mathrm{L1}}+$H$_2$. Vertical cyan (pulse-4) and magenta (pulse-2) lines show the instants of each pulse maximum.
  • ...and 2 more figures