We predict a highly stable and robust atomically thin gold monolayer with a hexagonal close packed lattice stabilized by metallic bonding with contributions from strong relativistic effects and aurophilic interactions. We have shown that the framework of the Au monolayer can survive 10 ps MD annealing simulations up to 1400 K. The framework is also able to survive large motions out of the plane. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk we observe significantly enhanced energy per bond (0.94 vs. 0.52 eV per bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. It is a non-magnetic metal, and was found to be the global minima in the 2D space. Phonon dispersion calculations demonstrate high kinetic stability with no negative modes. This 2D gold monolayer corresponds to the top monolayer of the bulk Au(111) face-centered cubic lattice. The close-packed lattice maximizes the aurophilic interactions. We find that the electrons are completely delocalized in the plane and behave as 2D nearly free electron gas. We hope that the present work can inspire the experimental fabrication of novel free standing 2D metal systems.

Graphene and its analogues have some of the highest predicted melting points of any materials. Previous work estimated the melting temperature for freestanding graphene to be a remarkable 4510 K. However, this work relied on theoretical methods that do not accurately account for the role of bond breaking or complex bonding configurations in the melting process. Furthermore, experiments to verify these high melting points have been challenging. Practical applications of graphene and carbon nanotubes at high temperatures will require a detailed understanding of the behavior of these materials under these conditions. Therefore, we have used exclusively reliable ab initio molecular dynamics calculations to study the initial stages of melting of freestanding graphene monolayers between 4000 and 6000 K. To accommodate large defects, and for improved accuracy, we used a large 10 x 10 periodic unit cell. We find that the system can be heated up to 4500 K for 18 ps without melting, and 3-rings and short lived broken bonds (10-rings) are observed. At 4500 K, the system appears to be in a quasi-2D liquid state. At 5000 K, the system is starting to melt. During the 20 ps simulation, diffusion events are observed, leading to the creation of a 5775 defect. We calculate accurate excitation energies for these configurations, and the pair correlation function is presented. The modified Lindemann criterion was calculated. Graphene and nanotubes together with other proposed high melting point materials would be interesting candidates for experimental tests of melting in the weightless environment of space.