A molecular dynamics simulation on mechanical and thermodynamic properties of M_VIII-metals (Ni, Pd,...

Composite nanostructures formed by depositing M(VIII)-metals (Ni, Pd, Pt) on 6,6,12-graphyne (GY) are promising candidates for functional nanomaterial applications, yet the atomic-scale interfacial structure-property relationships remain poorly understood, particularly the joint effects of metal identity and temperature. This work systematically investigates the mechanical and thermodynamic properties of Ni/GY, Pd/GY, and Pt/GY composites across a representative temperature range (1 K, 50 K, 298 K) using classical molecular dynamics simulations. Radial distribution function analysis confirms robust interfacial bonding for all three metals, with Ni forming the shortest M-C bonds (2.08-2.17 Å) due to more effective d-orbital overlap. Coordination number analysis further quantifies the interfacial bonding strength, yielding coordination number values of 3.8-4.5 for Ni/GY versus 2.3-2.5 for Pd/GY and 2.6-3.0 for Pt/GY, independently confirming the stronger Ni-C interaction. A non-monotonic temperature dependence of local ordering is identified for Pd, attributed to thermally activated relaxation. Uniaxial tensile tests reveal that Ni/GY exhibits a strength peak at 50 K (118 GPa), arising from the interplay between thermal activation and interfacial bond disruption, whereas Pd/GY and Pt/GY show monotonic strength decrease with temperature. Young's moduli extracted from the elastic region (498-690 GPa) are consistent with available graphyne literature data. At 50 K and 298 K, the composite with the highest coordination number (Ni/GY) also exhibits the highest peak strength, while at 1 K the correlation breaks down due to insufficient thermal activation of the interfacial configuration, demonstrating that the mechanical response is jointly governed by interfacial bonding and temperature-dependent structural relaxation. The specific heat capacity of Ni/GY is calculated and compared with the classical Dulong-Petit limit. All key results are validated against available DFT and MD literature data, with deviations of 6-21% for bond distances and reasonable agreement for mechanical and thermal properties, confirming the physical reliability of the simulations.

All molecular dynamics simulations were performed using the LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) software. The simulation cell (20 × 16 × 7 ų) employed periodic boundary conditions in the x and y directions and a fixed boundary with > 15 Å vacuum in the z direction. Interatomic interactions were described by the embedded-atom method (EAM) potential for the metal atoms (Ni, Pd, Pt), the adaptive intermolecular reactive empirical bond order (AIREBO) potential for carbon-carbon interactions within 6,6,12-graphyne, and the Lennard-Jones potential for the metal-carbon interface. Systems were equilibrated in the isothermal-isobaric (NPT) ensemble for 1 ns using the Nosé-Hoover thermostat and barostat. NPT simulations were used for uniaxial tensile testing and specific heat capacity calculations. Interfacial structure was characterized through radial distribution function analysis, and atomic configurations were visualized using the OVITO software.