Xueyao Zhou

High-Dimensional Atomistic Neural Network Potentials for Molecule–Surface Interactions: HCl Scattering from Au(111)

Ab initio molecular dynamics (AIMD) simulations of molecule-surface scattering allow first-principles characterization of the dynamics. However, the large number of density functional theory calculations along the trajectories is very costly, limiting simulations of long-time events and giving rise to poor statistics. To avoid this computational bottleneck, we report here the development of a high-dimensional molecule-surface interaction potential energy surface (PES) with movable surface atoms, using a machine learning approach. With 60 degrees of freedom, this PES allows energy transfer between the energetic impinging molecule and thermal surface atoms. Classical trajectory calculations for the scattering of DCl from Au(111) on this PES are found to agree well with AIMD simulations, with ∼105-fold acceleration. Scattering of HCl from Au(111) is further investigated and compared with available experimental results.

Non-Adiabatic Effects on Excited States of Vinylidene Observed with Slow Photoelectron Velocity-Map Imaging

High-resolution slow photoelectron velocity-map imaging spectra of cryogenically cooled X̃2B2 H2CC- and D2CC- in the region of the vinylidene triplet excited states are reported. Three electronic bands are observed and, with the assistance of electronic structure calculations and quantum dynamics on ab initio-based near-equilibrium potential energy surfaces, are assigned as detachment to the [Formula: see text] 3B2 (T1), b̃ 3A2 (T2), and à 1A2 (S1) excited states of neutral vinylidene. This work provides the first experimental observation of the à singlet excited state of H2CC. While regular vibrational structure is observed for the ã and à electronic bands, a number of irregular features are resolved in the vicinity of the b̃ band vibrational origin. High-level ab initio calculations suggest that this anomalous structure arises from a conical intersection between the ã and b̃ triplet states near the b̃ state minimum, which strongly perturbs the vibrational levels in the two electronic states through nonadiabatic coupling. Using the adiabatic electron affinity of H2CC previously measured to be 0.490(6) eV by Ervin and co-workers [J. Chem. Phys. 1989, 91, 5974], term energies for the excited neutral states of H2CC are found to be T0(ã 3B2) = 2.064(6), T0(b̃ 3A2) = 2.738(6), and T0(à 1A2) = 2.991(6) eV.

Ab initio molecular dynamics study of the Eley-Rideal reaction of H + Cl–Au(111) → HCl + Au(111): Impact of energy dissipation to surface phonons and electron-hole pairs

The reaction between an impinging H atom and a Cl atom adsorbed on Au(111), which is a prototype for the Eley-Rideal mechanism, is investigated using ab initio molecular dynamics at different incidence angles. The reaction yielding gaseous HCl with large internal excitation proceeds via both direct and hot-atom mechanisms. Significant energy exchange with both surface phonons and electron-hole pairs has been observed. However, their impact on the reactivity and final state distributions was found to be limited, thanks to the large exothermicity and small barrier of the reaction.

Ultrafast Excited-State Dynamics of Cytosine Aza-Derivative and Analogues

Excited state dynamics of 5-azacytosine (5-AC), 2,4-diamino-1,3,5-triazine (2,4-DT), and 2-amino-1,3,5-triazine (2-AT) were comprehensively investigated by steady state absorption, fluorescence, and femtosecond transient absorption measurements. Time-dependent density functional theory (TDDFT) calculations were performed to help assign the absorption bands and understand the excited state decay mechanisms. The experimental results of excited singlet state dynamics for 5-AC, 2,4-DT, and 2-AT with femtosecond time resolution were reported for the first time. Two distinct decay pathways, with ∼1 ps and tens of picosecond lifetimes, were observed in 5-AC. Only one decay pathway with 17 ps lifetime was observed in 2,4-DT while an emissive state was found in 2-AT. TDDFT calculations suggest that 5-AC has a dark nπ* (S1) state below the first allowed ππ* (S2) state, which leads to the ultrafast decay of the ππ* state. In 2,4-DT, there is no dark nπ* state below the bright ππ* (S1) state and the 17 ps lifetime is assigned to the relaxation from the ππ* (S1) state to ground state. Two dark nπ* states (S1 and S2) were found in 2-AT, which exhibits much more complex excited state dynamics compared with the other two. Photoluminescence in 2-AT has been confirmed to be fluorescence emission from its bright ππ* (S3) state. Our results strongly suggest that electronic structures are very sensitive to the substitution on the triazine ring and that the photophysical properties of nucleic acid analogues depend highly on their molecular structures.

Vibrational control of selective bond cleavage in dissociative chemisorption of methanol on Cu(111)

Controlling product branching ratios in a chemical reaction represents a desired but difficult achievement in chemistry. In this work, we demonstrate the first example of altering the branching ratios in a multichannel reaction, i.e., methanol dissociative chemisorption on Cu(111), via selectively exciting specific vibrational modes. To this end, we develop a globally accurate full-dimensional potential energy surface for the CH3OH/Cu(111) system and perform extensive vibrational state-selected molecular dynamics simulations. Our results show that O–H/C–H/C–O stretching vibrational excitations substantially enhance the respective bond scission processes, representing extraordinary bond selectivity. At a given total energy, the branching ratio of C–O/C–H dissociation can increase by as large as 100 times by exciting the C–O stretching mode which possesses an unprecedentedly strong vibrational efficacy on reactivity. This vibrational control can be realized by the well-designed experiment using a linearly polarized laser.Dissociative chemisorption of methanol on metal surfaces is a key step for hydrogen production. Here the authors use quasi-quantized molecular dynamics simulations to alter the branching ratios for methanol dissociative chemisorption on Cu(111) via selectively exciting specific vibrational modes.

Effects of surface motion and electron-hole pair excitations in CO2 dissociation and scattering on Ni(100)

The energy transfer between different channels is an important aspect in chemical reactions at surfaces. We investigate here in detail the energy transfer dynamics in a prototypical system, i.e., reactive and nonreactive scattering of CO2 on Ni(100), which is related to heterogeneous catalytic processes with Ni-based catalysts for CO2 reduction. On the basis of our earlier nine-dimensional potential energy surface for CO2/Ni(100), dynamical calculations have been done using the generalized Langevin oscillator (GLO) model combined with local density friction approximation (LDFA), in which the former accounts for the surface motion and the latter accounts for the low-energy electron-hole pair (EHP) excitation. In spite of its simplicity, it is found that the GLO model yields quite satisfactory results, including the significant energy loss and product energy disposal, trapping, and steering dynamics, all of which agree well with the ab initio molecular dynamics ones where many surface atoms are explicitly involved with high computational cost. However, the GLO model fails to describe the reactivity enhancement due to the lattice motion because it intrinsically does not incorporate the variance of barrier height on the surface atom displacement. On the other hand, in LDFA, the energy transferred to EHPs is found to play a minor role and barely alter the dynamics, except for slightly reducing the dissociation probabilities. In addition, vibrational state-selected dissociative sticking probabilities are calculated and previously observed strong mode specificity is confirmed. Our work suggests that further improvement of the GLO model is needed to consider the lattice-induced barrier lowering.