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We studied a critical size of copper (Cu) clusters where the electronic effect and the size effect on the ground state structure become weaker. Identification of these transitional clusters thus provides with the means to efficiently determine the ground state structure of large clusters using density functional theory (DFT). Our work indicated that beyond the critical size of the transitional cluster, geometrical effects become important, and the putative global minimum structure obtained from an empirical method can be used as an initial structure to determine the true ground state structure using DFT. Structural evolution of ground states was also presented with an increase in the cluster size. To investigate low-lying structures of Cu, we used a Monte Carlo (MC)-simulated annealing method that employs the aggregate-volume-bias MC algorithm. Incorporated in the MC method is an embedded atom method potential developed by the authors. This search method identified the low-lying structures in an effective manner.

When hydrogen is produced from a biomass or coal gasifier, it is necessary to purify it from syngas streams containing components such as CO, CO2, N2, CH4, and other products. Therefore, a challenge related to hydrogen purification is the development of hydrogen-selective membranes that can operate at elevated temperatures and pressures, provide high fluxes, long operational lifetime, and resistance to poisoning while still maintaining reasonable cost. Palladium-based membranes have been shown to be well suited for these types of high-temperature applications and have been widely utilized for hydrogen separation. Palladium's unique ability to absorb a large quantity of hydrogen can also be applied in various clean energy technologies, like hydrogen fuel cells. In this paper, a fully analytical interatomic embedded atom method (EAM) potential for the Pd-H system has been developed, that is easily extendable to ternary Palladium-based hydride systems, such as Pd-Cu-H and Pd-Ag-H. The new potential has fewer fitting parameters than previously developed EAM Pd-H potentials and is able to accurately predict the cohesive energy, lattice constant, bulk modulus, elastic constants, melting temperature, and the stable Pd-H structures in molecular dynamics (MD) simulations with various hydrogen concentrations. The EAM potential also well predicts the miscibility gap, the segregation of the palladium hydride system into dilute (α), and concentrated (β) phases.

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