Applications and Advances in Machine Learning Force Fields.

Force fields (FFs) form the basis of molecular simulations and have significant implications in diverse fields such as materials science, chemistry, physics, and biology. A suitable FF is required to accurately describe system properties. However, an off-the-shelf FF may not be suitable for certain specialized systems, and researchers often need to tailor the FF that fits specific requirements. Before applying machine learning (ML) techniques to construct FFs, the mainstream FFs were primarily based on first-principles force fields (FPFF) and empirical FFs. However, the drawbacks of FPFF and empirical FFs are high cost and low accuracy, respectively, so there is a growing interest in using ML as an effective and precise tool for reconciling this trade-off in developing FFs. In this review, we introduce the fundamental principles of ML and FFs in the context of machine learning force fields (MLFF). We also discuss the advantages and applications of MLFF compared to traditional FFs, as well as the MLFF toolkits widely employed in numerous applications.

Tuning Chirality of Self-Assembled PTCDA Molecules on a Au(111) Surface by Na Coordination.

Chiral nanostructures are much desired in many applications, such as chiral sensing, chiroptics, chiral electronics, and asymmetric catalysis. In building chiral nanostructures, the on-surface metal-organic self-assembly is naturally suitable in obtaining atomically precise structures, but that is under the premise that there are enantioselective assembly strategies to create large-scale homochiral networks. Here, we report an approach to build chiral metal-organic networks using 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) molecules and low-cost sodium chloride (NaCl) in a controllable manner on Au(111). The chirality induction and transfer processes during network evolution with increased Na ion ratios were captured by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) methodologies. Our findings show that Na ion incorporation into achiral PTCDA molecules partially breaks intermolecular hydrogen bonds and coordinates with carboxyl oxygen atoms, which initiates a collective sliding motion of PTCDA molecules along specific directions. Consequently, "molecular columns" linked by hydrogen bonds were formed in the rearranged Na-PTCDA networks. Notably, the direction of Na ion incorporation determines the chiral characteristic by guiding the sliding direction of the molecular columns, and chirality can be transferred from Na0.5PTCDA to Na1PTCDA networks. Furthermore, our results indicate that the chirality transferring process is disrupted when intermolecular hydrogen bonds are entirely replaced by Na ions at a high Na dopant concentration. Our study provides fundamental insights into the mechanism of coordination-induced chirality in metal-organic self-assemblies and offers potential strategies for synthesizing large homochiral metal-organic networks.

Progress on Two-Dimensional Transitional Metal Dichalcogenides Alloy Materials: Growth, Characterisation, and Optoelectronic Applications.

Two-dimensional (2D) transitional metal dichalcogenides (TMDs) have garnered remarkable attention in electronics, optoelectronics, and hydrogen precipitation catalysis due to their exceptional physicochemical properties. Their utilisation in optoelectronic devices is especially notable for overcoming graphene's zero-band gap limitation. Moreover, TMDs offer advantages such as direct band gap transitions, high carrier mobility, and efficient switching ratios. Achieving precise adjustments to the electronic properties and band gap of 2D semiconductor materials is crucial for enhancing their capabilities. Researchers have explored the creation of 2D alloy phases through heteroatom doping, a strategy employed to fine-tune the band structure of these materials. Current research on 2D alloy materials encompasses diverse aspects like synthesis methods, catalytic reactions, energy band modulation, high-voltage phase transitions, and potential applications in electronics and optoelectronics. This paper comprehensively analyses 2D TMD alloy materials, covering their growth, preparation, optoelectronic properties, and various applications including hydrogen evolution reaction catalysis, field-effect transistors, lithium-sulphur battery catalysts, and lasers. The growth process and characterisation techniques are introduced, followed by a summary of the optoelectronic properties of these materials.