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First-principles calculations within density functional theory (DFT) with the projector augmented wave (PAW) technique were used to investigate the stabilities of intermetallics in the Au-Rb system at 0 K. Four intermetallics: Au 7 Rb 3 , Au 3 Rb 2 , Au 5 Rb and AuRb were investigated in their observed experimental structures. The Au 2 Rb compound, reported in the Au-Rb phase diagrams without specifying explicitly its structure, was also investigated by inspecting several hypothetical structures. A suspect compound (AuRb 2 ) was also investigated. Results show that: (i) The Au 3 Rb 2 and Au 7 Rb 3 compounds, which were never reported in any Au-Rb phase diagram, are stable at 0 K. (ii) The Au 2 Rb compound is not a ground state for all the tested structures. (iii) Stability of the Au 5 Rb and AuRb compounds was confirmed. (iv) The new compound AuRb 2 , not yet reported experimentally, is found mechanically stable at 0 K.

In this paper, we present a study of the structural stability of BaSi 2 under high pressure based on first-principles calculations using the projector augmented wave method and generalized gradient approximation as implemented in the ABINIT code. The equations of state of three known polymorphs of BaSi 2 and four candidate structures are calculated along with their structural parameters and their enthalpies of formation. A new polymorph of BaSi 2, not yet reported experimentally, is found to be more stable than all the other structures at high pressure and 0 K. It corresponds to the MgZn 2-type (h) hexagonal structure with hP12 Pearson symbol (space group: P63/mmc. The stiffness coefficients Bij and elastic properties including bulk modulus B0 with its first and second pressure derivative (B′, B′′), Young's modulus (E) and Poisson's ratio (ν) are computed using the stress–strain method.