Dong Hui Zhang

Accurately solving the nuclear Schrödinger equation for molecular complexes exhibiting noncovalent interactions remains a challenge due to the exponential scaling of basis sets and the presence of strongly anharmonic, large-amplitude motions. Recently, we proposed a neural network (NN) method to tackle high-dimensional vibrational problems and successfully applied it to C3H8 in full dimensionality; however, applying the method to molecular complexes has been hindered by difficulties in representing delocalized wave functions across multiple minima. In this work, we present a substantially improved NN-based methodology that overcomes these limitations through two key developments: (i) a novel NN architecture specifically designed to capture the asymptotic behavior and delocalization characteristics of weakly bound complexes, and (ii) an efficient training protocol that optimizes the variance of local energies. We demonstrate that this approach achieves subcm–1 accuracy for the vibrational ground and excited states of CH4 with substantially fewer parameters than the previous method requires. Crucially, for the prototypical water dimer (H2O)2, the new method successfully computes both ground state and intramolecular excited states with ∼1 cm–1 accuracy using ∼6000 NN parameters. This work establishes a robust and scalable framework for performing full-dimensional, fully coupled vibrational calculations on molecular complexes, providing an efficient approach for accurate spectroscopic predictions of such systems.

The negative-ion photoelectron spectrum of the cyanocyclopentadienide anion is simulated using a multimode vibronic-coupling approach based on a two-state quasi-diabatic Hamiltonian, Hd. This Hamiltonian accurately describes the region near the ab initio equilibrium geometry of the neutral ground state, as well as the minimum-energy crossing point on the conical intersection seam, which lies only approximately 1600 cm–1 above the ground-state minimum. Comparison with the experimental spectra allows the X and A peaks to be assigned to the ground vibrational levels of the 2B1 and 2A2 diabatic states, respectively. Significant mixing of harmonic multimode basis functions induced by the conical intersection is evident even for these low-lying X and A peaks. Moreover, peaks X and A show the strongest enhancement in most of the resonant photoelectron spectra, suggesting that the Δν = −1 propensity rule may extend to multiple electronic states.

The hydrogen abstraction reaction H + CH2D2 → H2 + CHD2 serves as an essential benchmark for polyatomic reaction dynamics, yet its lack of C3v symmetry has precluded full-dimensional quantum mechanical treatments. Here, we report the first full-dimensional (12D) time-dependent wave packet study of this reaction on an accurate potential energy surface. Our calculations reveal a striking hierarchy of mode-specific efficacy: excitation of the reacting CH2 stretching modes enhances reactivity by factors of 8.7 and 7.6, while vibrational energy deposited into the spectator CD2 modes proves less effective than translational energy. The torsional and rocking motions exhibit moderate promotional effects. At combustion-relevant temperatures, CH2 stretching excitations collectively contribute over 53% of the thermal rate constant at 2000 K. This work establishes the first rigorous quantum mechanical baseline for mode-selective chemistry in an asymmetric methane isotopologue and provides a powerful framework for elucidating bond-specific dynamics in complex polyatomic systems.

Quantum dynamics calculations scale steeply with system size, rendering calculations on a classical computer intractable for complex systems. While quantum computing offers a natural solution, its application to nuclear quantum dynamics has been scarce. Here, we present a quantum algorithm to study photodissociation dynamics on quantum computers, benchmarked on the NOCl molecule. The wave function is propagated via a split-operator method, utilizing the quantum Fourier transform and unitary transformation matrix to switch representations. To impose outgoing boundary conditions on a truncated grid, we use a nonunitary absorbing potential propagator, implemented through a dilation scheme. The photodissociation cross section is calculated from the autocorrelation function, which is extracted using the Hadamard test. Our quantum computing results agree well with benchmarks under ideal conditions, and we further demonstrate that the algorithm is robust to noise and statistical sampling errors, indicating its promise for application of noisy devices for quantum dynamics studies.

We present the first six-dimensional quantum dynamics study of HCl dissociative chemisorption on Pt(111) based on an accurate neural network potential energy surface. The transition state H-Cl bond is stretched by Δr = 0.40 to 2.82 bohr, significantly shorter than those for HCl on Au(111) and Ag(111). This places HCl/Pt(111) in a distinct central barrier regime, leading to two atypical outcomes. First, unlike on Au(111) or Ag(111), where the top site is two orders of magnitude less reactive, the dissociation probability at the top site on Pt(111) is comparable to that at other sites. Second, translational energy is consistently more effective than vibrational excitation, with vibrational efficacy η < 1 for v = 1 and 2 across the entire total energy range. In contrast, rotational effects remain unaffected, showing the same helicopter preference and reduced rotational efficacy as on monometallic surfaces. By comparing eleven HCl + metal systems, we reveal a clear quantitative trend. When Δr is 0.40-0.50 bohr, η remains below unity. When Δr reaches 1.32 bohr, η is always above unity. This provides a geometric rationalization of Polanyi's early/late dichotomy.

Artificial neural networks are universal function approximators and have shown great ability in computing the ground-state energy of the electronic Schrödinger equation, yet have not established themselves as a practical and accurate approach for solving the vibrational Schrödinger equation for realistic polyatomic molecules. Here, we propose an efficient neural-network approach for solving the vibrational Schrödinger equation and provide a detailed illustration using the methane molecule. To demonstrate the power of the proposed method, we then apply it to propane, an 11-atom molecule with 27 vibrational degrees of freedom. Using a neural network with fewer than 15,000 parameters, we obtain the ground-state energy within 1 cm ⁻¹ of the reference value obtained from a diffusion Monte Carlo calculation, as well as vibrational energies for three excited states involving C-C-C stretching/bending modes that agree with the corresponding experimental values within the experimental uncertainties. The proposed method is expected to provide highly accurate vibrational energies and wavefunctions for molecules with more than 20 atoms.

Accurately solving the nuclear Schrödinger equation for molecular complexes exhibiting noncovalent interactions remains a challenge due to the exponential scaling of basis sets and the presence of strongly anharmonic, large-amplitude motions. Recently, we proposed a neural network (NN) method to tackle high-dimensional vibrational problems and successfully applied it to C ₃ H ₈ in full dimensionality; however, applying the method to molecular complexes has been hindered by difficulties in representing delocalized wave functions across multiple minima. In this work, we present a substantially improved NN-based methodology that overcomes these limitations through two key developments: (i) a novel NN architecture specifically designed to capture the asymptotic behavior and delocalization characteristics of weakly bound complexes, and (ii) an efficient training protocol that optimizes the variance of local energies. We demonstrate that this approach achieves sub‑cm ^-1 accuracy for the vibrational ground and excited states of CH ₄ with substantially fewer parameters than the previous method requires. Crucially, for the prototypical water dimer (H ₂ O) ₂ , the new method successfully computes both ground state and intramolecular excited states with ~ 1 cm ^-1 accuracy using ~6,000 NN parameters. This work establishes a robust and scalable framework for performing full-dimensional, fully coupled vibrational calculations on molecular complexes, paving the way for accurate spectroscopic predictions of systems previously deemed intractable.

A global ground electronic state potential energy surface for the OH + NH ₃ reaction is constructed. The PES accurately describes not only the hydrogen abstraction channel, but also the NH ₂ OH formation channel.

Full-dimensional simulations reveal roaming as a general, nontraditional pathway. Its distinctive dynamics and energy redistribution significantly affect product branching and reaction rates, beyond the conventional minimum-energy-path paradigm.