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We describe a local surrogate model for use in conjunction with global structure search methods. The model follows the Gaussian approximation potential (GAP) formalism and is based on a the smooth overlap of atomic positions descriptor with sparsification in terms of a reduced number of local environments using mini-batch $k$-means. The model is implemented in the Atomistic Global Optimization X framework and used as a partial replacement of the local relaxations in basin hopping structure search. The approach is shown to be robust for a wide range of atomistic system including molecules, nano-particles, surface supported clusters and surface thin films. The benefits in a structure search context of a local surrogate model are demonstrated. This includes the ability to transfer learning from smaller systems as well as the possibility to perform concurrent multi-stoichiometry searches., Comment: 12 pages, 11 figures

Fragmentation is an important decay mechanism for polycyclic aromatic hydrocarbons (PAHs) under harsh interstellar conditions and represents a possible formation pathway for small molecules such as H2, C2H2, C2H4. Our aim is to investigate the dissociation mechanism of superhydrogenated PAHs that undergo energetic processing and the formation pathway of small hydrocarbons. We obtain, experimentally, the mass distribution of protonated tetrahydropyrene (C16H15 , py+5H+) and protonated hexahydropyrene (C16H17+, py+7H+) upon collision induced dissociation (CID). The IR spectra of their main fragments are recorded by infrared multiple-photon dissociation (IRMPD). Extended tight-binding (GFN2-xTB) based molecular dynamics simulations are performed in order to provide the missing structure information in experiment and identify fragmentation pathways. The pathways for fragmentation are further investigated at a hybrid-density functional theory (DFT) and dispersion corrected level. A strong signal for loss of 28 mass units of py+7H+ is observed both in the CID experiment and the MD simulation, while py+5H+ shows negligible signal for the product corresponding to a mass loss of 28. The 28 mass loss from py+7H+ is assigned to the loss of ethylene (C2H4) and a good fit between the calculated and experimental IR spectrum of the resulting fragment species is obtained. Further DFT calculations show favorable kinetic pathways for loss of C2H4 from hydrogenated PAH configurations involving three consecutive CH2 molecular entities. This joint experimental and theoretical investigation proposes a chemical pathway of ethylene formation from fragmentation of superhydrogenated PAHs. This pathway is sensitive to hydrogenated edges (e.g. the degree of hydrogenation and the hydrogenated positions). The inclusion of this pathway in astrochemical models may improve the estimated abundance of ethylene., 11 pages, 6 figures

Dimerization of polycyclic aromatic hydrocarbons (PAHs) is an important, yet poorly understood, step in the on-surface synthesis of graphene (nanoribbon), soot formation, and growth of carbonaceous dust grains in the interstellar medium (ISM). The on-surface synthesis of graphene and the growth of carbonaceous dust grains in the ISM require the chemical dimerization in which chemical bonds are formed between PAH monomers. An accurate and cheap method of exploring structure rearrangements is needed to reveal the mechanism of chemical dimerization on surfaces. This work has investigated the chemical dimerization of two dehydrogenated PAHs (coronene and pentacene) on graphene via an evolutionary algorithm augmented by machine learning surrogate potentials and a set of customized structure operators. Different dimer structures on surfaces have been successfully located by our structure search methods. Their binding energies are within the experimental errors of temperature programmed desorption measurements. The mechanism of coronene dimer formation on graphene is further studied and discussed., 8 pages, 6 figures

Electrochemical reduction of CO2 to carbon-containing fuels possesses the potential to solve the environmental issues caused by excess CO2 in the atmosphere. Herein, we introduce a ternary Au-CDots-C3N4 electrocatalyst for efficiently reducing CO2 to CO. The ternary catalyst exhibited significantly enhanced activity and stability for CO2 electroreduction in comparison with pure Au NPs. The Au-CDots-C3N4 electrocatalyst demonstrates a high CO FE of ∼79.8% at −0.5 V and a 2.8-fold enhancement of current density (with the Au loading only 4 wt %) at −1.0 V relative to pure Au NPs. The DFT calculations and experimental observations indicate that the high activity toward CO2RR originates from the synergetic effect among Au NPs, CDots, and C3N4 and the capability of H+ and CO2 adsorption from CDots. The long-term stability tests demonstrate that the electrocatalyst can be used for over 8 h without obvious deactivations and maintained its activity over 60 days under normal conditions.

Growth and meat quality are concerned issues in aquaculture. The inhibition of MSTN can lead to significant muscle proliferation in mammals, as well as a decrease in muscle fat content. In fish, the effect of MSTN inhibition on muscle fat content is ambiguous. In this study, we constructed transgenic red carp with Larimichthys crocea MSTN1 propeptide (LcMSTN1 propeptide) to study how the inhibition of MSTN1 affects the growth and muscle fat content in fish. Southern Blotting showed that LcMSTN1 propeptide was integrated into the red carp genome. In muscle tissue, the expression of MSTN1 propeptide in transgenic red carp was significantly higher than that of non-transgenic red carp (P

The hydrogen evolution reaction (HER) is a fundamental electrochemical reaction to produce hydrogen gas from the electrolysis of water, and has been regarded as an attractive solution to many energy challenges. In the past few decades, platinum has been widely demonstrated to split water into hydrogen gas at high reaction rates and low overpotentials. Nevertheless, decreasing the loading of Pt in the designed electrocatalysts is very significant. However, with low Pt loading, it is challenging to maintain excellent catalytic performance. Here we report a Pt–Au–Si ternary nanocomposite as a highly active catalyst for the HER. The optimal composition of Pt–Au–Si was determined to be 7.2 : 31.3 : 61.5 (Pt : Au : Si, mass ratio) with a Tafel slope of only 24 mV dec−1. To be specific, the mass activity of the Pt–Au–SiNW-2 catalyst was 6.5 fold that of a 40 wt% Pt/C catalyst at an overpotential of 60 mV. More importantly, the cathodic current density even surpassed 40 wt% Pt/C when the overpotential was larger than 0.17 V (the corresponding current density was 108 mA cm−2). The outstanding catalytic performance might be derived from the synergy of the respective properties of the three components: the fast hydrogen adsorption rate on Pt, the quick migration of the adsorbed hydrogen atoms on Au and the rapid hydrogen evolution rate on Si. This research opens up a novel strategy to prepare highly efficient catalysts for electrochemical hydrogen evolution reactions.

Functionalization of graphene on Ir(111) is a promising route to modify graphene by chemical means in a controlled fashion at the nanoscale. Yet, the nature of such functionalized sp(3) nanodots remains unknown. Density functional theory (DFT) calculations alone cannot differentiate between two plausible structures, namely true graphane and substrate stabilized graphane-like nanodots. These two structures, however, interact dramatically differently with the underlying substrate. Discriminating which type of nanodots forms on the surface is thus of paramount importance for the applications of such prepared nanostructures. By comparing X-ray standing wave measurements against theoretical model structures obtained by DFT calculations we are able to exclude the formation of true graphane nanodots and clearly show the formation graphane-like nanodots.

The demand for catalyst with higher activity and higher selectivity is still a central issue in current material science community. On the basis of first-principles calculations, we demonstrate that the catalytic performance of the Pd-TiO2 hybrid nanostructures can be selectively promoted or depressed by choosing the suitable shaped Pd and TiO2 nanocrystals. To be more specific, the catalytic activities of Pd nanoparticles enclosed by (100) or (111) facets can be promoted more significantly when dosed on the TiO2(001) than on TiO2(101) under irradiation. Such theoretical prediction has then been further verified by the experimental observations in which the Pd(100)-TiO2(001) composites exhibit the highest catalytic performance toward the activation of oxygen among all the other shaped hybrid nanostructures. As a result, the selection of facets of support materials can provide an extra tuning parameter to control the catalytic activities of metal nanoparticles. This research opened up a new direction for designing and preparing catalysts with enhanced catalytic performance.

Surface-supported coupling reactions between 1,3,5-tris(4-formylphenyl)benzene and aromatic amines have been investigated on Au(111) using scanning tunneling microscopy under ultra-high-vacuum conditions. Upon annealing to moderate temperatures, various products, involving the discrete oligomers and the surface covalent organic frameworks, are obtained through thermal-triggered on-surface chemical reactions. We conclude from the systematic experiments that the stoichiometric composition of the reactants is vital to the surface reaction products, which is rarely reported so far. With this knowledge, we have successfully prepared two-dimensional covalently bonded networks by optimizing the stoichiometric proportions of the reaction precursors.

Recently, borophene was reported to be produced on silver surfaces. We employed density functional theory and electronic transport calculations to investigate the stabilities, electronic structures and transport properties of borophene nanoribbons. The stability of a borophene nanoribbon increases with its width and only the lined-edged borophene nanoribbons are stable in the free-standing form. Such anisotropic stability dependence is ascribed to the large scale delocalization of π electrons along the boron rows. In particular, all line-edge borophene nanoribbons undergo edge reconstructions, in which the out-of-plane bulking edge atoms are reconstructed to form quasi planar edge structures. Such edge reconstructions have not yet been reported, which is critical for the formation of boron nanostructrues. Subsequent electronic transport calculations based on a non-equilibrium Green’s function indicated that line-edge borophene nanoribbons exhibit low-resistivity Ohmic conductance. Our results indicated that the line-edge borophene nanoribbons present remarkable properties (high thermal stabilities, Ohmic conductance with low electrical resistivity and good rigidities) and are promising for applications as one-dimensional electrical connections in compact nanoscale circuits.