High performance global exploration of isomers and isomerization channels on quantum chemical potential energy surface of H5 C2 NO2

A highly accurate full-dimensional ab initio potential surface for the rearrangement of methylhydroxycarbene (H3C-C-OH)

We report here a full-dimensional machine learning global potential surface (PES) for the rearrangement of methylhydroxycarbene (H₃C-C-OH, 1t). The PES is trained with the fundamental invariant neural network (FI-NN) method on 91 564 ab initio energies calculated at the UCCSD(T)-F12a/cc-pVTZ level of theory, covering three possible product channels. FI-NN PES has the correct symmetry properties with respect to permutation of four identical hydrogen atoms and is suitable for dynamics studies of the 1t rearrangement. The averaged root mean square error (RMSE) is 11.4 meV. Six important reaction pathways, as well as the energies and vibrational frequencies at the stationary geometries on these pathways are accurately preproduced by our FI-NN PES. To demonstrate the capacity of the PES, we calculated the rate coefficient of hydrogen migration in -CH₃ (path A) and hydrogen migration of -OH (path B) with instanton theory on this PES. Our calculations predicted the half-life of 1t to be 95 min, which is excellent in agreement with experimental observations.

Artificial Neural Network-Derived Unified Six-Dimensional Potential Energy Surface for Tetra Atomic Isomers of the Biogenic [H, C, N, O] System

Recognition of different structural patterns in different potential energy surface regions, such as in isomerizing quasilinear tetra atomic molecules, is important for understanding the details of underlying physics and chemistry. In this respect, using three variants of artificial neural networks (ANNs), we investigated the six-dimensional (6-D) singlet potential energy surfaces (PES) of tetra atomic isomers of the biogenic [H, C, N, O] system. At first, we constructed a separate ANN potential for each of the studied isomers. In the next step, a comparative assessment of the separate ANN models led to the setting up of a unified 6-D singlet PES equally and accurately describing all studied isomers. The constructed unified model yields relative energies comparable to those obtained either from the gold standard CCSD(T) method or from separate ANNs for each of the studied isomers. The accuracy of the unified singlet PES is on the order of 10^-4 Hartrees (0.1 kcal/mol). The developed PES in this work captures the main features of nonlinear and quasilinear tetra atomic isomers of this biogenic system.

Global Search for Stable C4H5NO Compounds-Guinness Molecules and Stability Islands

Global reaction route mapping (GRRM) analysis for compounds with the formula C₄H₅NO allowed for the detection of the corresponding "Guinness molecules" 000 and 001, as well as around 150 other stable minima of the same composition. The results suggest that compounds of similar functionality form a kind of "Stability Island" with their free energies of formation falling within s relatively limited range.

Comprehensive Search of Stable Isomers of Alanine and Alanine Precursors in Prebiotic Syntheses

Enantiomeric excesses of l-amino acids have been detected in meteorites; however, their molecular mechanism and prebiotic syntheses are still a matter of debate. To elucidate the origin of homochirality, alanine and the chiral precursors formed in prebiotic processes were investigated with regard to their stabilities among their isomers by employing the minimum energy principle, namely, the abundancy of a molecule in the interstellar medium is directly correlated to the stability among isomers. To facilitate the search for possible isomers, we developed a new isomer search algorithm, the random connection method, and performed a thorough search for all the stable isomers within a given chemical formula. We found that alanine and most of its precursors are located at higher energy by more than 5.7 kcal mol^-1, with respect to the most stable isomer that consists of a linear-chain structure, whereas only the 2-aminopropanenitrile is the most stable isomer among all others possible. The inherent stability of the α-amino nitrile suggests that the 2-aminopropanenitrile is the dominant contribution in the formation of the common enantiomeric excess over α-amino acids.