Communication: Fitting potential energy surfaces with fundamental invariant neural network

A more flexible neural network (NN) method using the fundamental invariants (FIs) as the input vector is proposed in the construction of potential energy surfaces for molecular systems involving identical atoms. Mathematically, FIs finitely generate the permutation invariant polynomial (PIP) ring. In combination with NN, fundamental invariant neural network (FI-NN) can approximate any function to arbitrary accuracy. Because FI-NN minimizes the size of input permutation invariant polynomials, it can efficiently reduce the evaluation time of potential energy, in particular for polyatomic systems. In this work, we provide the FIs for all possible molecular systems up to five atoms. Potential energy surfaces for OH3 and CH4 were constructed with FI-NN, with the accuracy confirmed by full-dimensional quantum dynamic scattering and bound state calculations. Published by AIP Publishing

An accurate full-dimensional potential energy surface and quasiclassical trajectory dynamics of the H + H2O2 two-channel reaction

We report a new full-dimensional potential energy surface (PES) of the H + H2O2 reaction, covering both H-2 + HO2 and OH + H2O product channels. The PES was constructed using the recently proposed fundamental invariant neural network (FI-NN) approach based on roughly 110000 ab initio energy points by high level UCCSD(T)-F12/aug-cc-pVTZ calculations. The small fitting error (5.7 meV) and various tests imply a faithful representation of the discrete ab initio data over a large configuration space. Extensive quasiclassical trajectory (QCT) calculations were carried out on the new PES at a collision energy (E-c) of 15.0 kcal mol(-1). The reaction yields dominantly OH + H2O, because of the lower reaction barrier and much larger reaction exothermicity (approximate to 71 kcal mol(-1)) for this channel. Due to the exit barrier of both reaction channels, the most available energy is partitioned into the translational motion of the products. Considerable vibrational excitations of the H2O product are seen, particularly for the symmetric stretching and bending modes. The angular distributions show predominantly backward scattering, which is consistent with the direct rebound mechanism

Full-dimensional quantum dynamics study of the H-2 + C2H -> H + C2H2 reaction on an ab initio potential energy surface

This work performs a time-dependent wavepacket study of the H-2 + C2H -> H + C2H2 reaction on a new ab initio potential energy surface (PES). The PES is constructed using neural network method based on 68 478 geometries with energies calculated at UCCSD(T)-F12a/aug-cc-pVTZ level and covers H-2 + C2H H + C2H2, H + C2H2 -> HCCH2, and HCCH2 radial isomerization reaction regions. The reaction dynamics of H-2 + C2H -> H + C2H2 are investigated using full-dimensional quantum dynamics method. The initial-state selected reaction probabilities are calculated for reactants in eight vibrational states. The calculated results showed that the H-2 vibrational excitation predominantly enhances the reactivity while the excitation of bending mode of C2H slightly inhibits the reaction. The excitations of two stretching modes of C2H molecule have negligible effect on the reactivity. The integral cross section is calculated with J-shift approximation and the mode selectivity in this reaction is discussed. The rate constants over 200-2000 K are calculated and agree well with the experimental measured values. Published by AIP Publishing

Toward Single-Cell Multiple-Strategy Processing Shift Register Powered by Phase-Change Memory Materials

Modern innovations are built on the foundation of computers. Compared to von Neumann architectures having separate storage and processing units, in‐memory operation utilizes the same primary structure for data storage and register operations, therefore promising to decrease the energy cost of computing in data centers significantly. While various studies centered on exploring novel device architectures, designing suitable material platforms is extremely challenging. Herein, all four material (M) states of a phase‐change material (PCM) in data storage and register operations are utilized and a combined M state‐based model framework for developing in‐memory operation is demonstrated, along with nonvolatile, reprogrammable single‐cell shift register operations. A previously unachieved multiple‐level‐per‐volt different‐initial‐state multilevel set process with further computing in the M state‐based platform is realized. The simplest case of a programmable shift register configuration is demonstrated with a serial‐in–serial‐out processing strategy, as well as more complex reprogrammable processing schemes using the M state‐type platform, showing previously unreported nonvolatile shift register types with multiple processing approaches. This paves the way for development of next‐generation low‐power‐electronic systems using two‐terminal‐based semiconductor materials

Theoretical and experimental investigations of rate coefficients of O(D-1) + CH4 at low temperature

The rate coefficients of the barrierless O(D-1) + CH4 reaction are determined both theoretically and experimentally at 50-296 K. For the calculations, ring polymer molecular dynamics (RPMD) simulations are performed on the basis of a new neural network potential energy surface (PES) in the reactant asymptotic part. Only the reactant asymptotic part of the PES is constructed because of its barrierless and exothermic properties. Experimentally, the reaction rate coefficients are measured using a supersonic flow reactor. Pulsed laser photolysis of O-3 molecules is used as the source of O(D-1) atoms, which are detected directly through vacuum ultraviolet laser induced fluorescence at 115 nm. The branching ratio for H atom production is measured by comparing the H atom yields of the O(D-1) + CH4 and O(D-1) + H-2 reactions. At T >= 75 K, good agreement between theoretical and experimental rate coefficients is found, while at 50 K, the larger difference is discussed in detail

Trapped Abstraction in the O(¹D) + CHD₃ → OH + CD₃ Reaction

Despite significant progress made in past decades, it is still challenging to elucidate dynamics mechanisms for polyatomic reactions, in particular, involving complex formation. The reaction of O­(¹D) with methane has long been regarded as a prototypical polyatomic system of direct insertion reaction in which the O­(¹D) atom can insert into the C–H bond of methane to form a “hot” methanol intermediate before decomposition. Here, we report a combined theoretical and experimental study on the O­(¹D) + CHD₃ reaction, on which good agreement between theory and experiment is achieved. Our study revealed that this complex-forming reaction actually proceeds via a trapped abstraction mechanism, rather than an insertion mechanism as has long been thought. We anticipate that this reaction mechanism should also be responsible for the reaction of O­(¹D) with ethane and propane, as well as many other chemical reactions with deep wells in the interaction region