Structural phase transition and superconductivity of ytterbium under high pressure

On the use of Monkhorst–Pack scheme to evaluate superconductivity and the issue of umklapp electron–phonon interactions

“…Consequently, we find T c = 0.19 K from the relation 2D 0 /k B T c = 3.52, that is Pd becomes a superconductor. In comparison, with the umklapp pairing scheme in eqn (15), we find a different a 2 F(n) shown as the shaded silhouette in the top part of Fig. 2, l = 0.199.…”

“…We test if our pairing scheme in eqn (15), which excludes an extensive range of phonons, ensures accurate superconductivity. We will perform a two-dimensional search to specify V(r) in eqn (21) to minimize the difference between the experimental and computational values of the superconducting tunnelling current shown in the bottom part of Fig.…”

“…8, the shaded silhouette represents the experimental a 2 F(n) from ref. 49 the histogram, arises from eqn (8) in turn arises from S(q) in eqn (15) and g c (q) in eqn (20) via V(r) in eqn (21). It enables us the solve the Eliashberg equation at T = 0 numerically provided we know the edge of the superconducting gap function, D 0 .…”

Tantalum Diboride: The Superhard and Metallic Boride

“…The structure prediction of TaB 2 under ambient pressure is performed by the CALYPSO method combined with the Vienna ab initio simulation package (VASP) . This effective method successfully searched the ground-state and metastable-state structures for various systems from zero-dimensional (0D) clusters to two-dimensional (2D) monolayers and to three-dimensional crystals. − During the structure prediction of TaB 2 , 70% of low-lying structures are collected as the specimens to create the candidate structures in the next generation, and the remaining 30% of structures are generated with some special restrictions, such as the symmetries, the bond lengths, and so forth. After 50 generations of structure searches, about 1200 to 1500 low-lying structures of TaB 2 are obtained at ambient pressure.…”

“…In this work, we perform comprehensive structure searches of TaB 2 by crystal structure analysis by the particle swarm optimization (CALYPSO) structural search method and first-principles calculations. − Our results show that two novel structures of TaB 2 with Cmmm and I 4 1 / amd symmetries can be metastable at ambient pressure, except for the well-known ground-state structure of the P 6/ mmm phase. The subsequent stress–strain calculations of the three structures indicate the abnormal stress responses of TaB 2 in many crystal planes, which are the apparent strain-stiffening behaviors along some main directions.…”