RESUMO
The electronic structure, interatomic bonding, and mechanical properties of two supercell models of Ni-based superalloys are calculated using ab initio density functional theory methods. The alloys, Haynes282 and Inconel740, are face-centered cubic lattices with 864 atoms and eleven elements. These multi-component alloys have very complex electronic structure, bonding and partial-charge distributions depending on the composition and strength of the local bonding environment. We employ the novel concept of total bond order density (TBOD) and its partial components (PBOD) to ascertain the internal cohesion that controls the intricate balance between the propensity of metallic bonding between Ni, Cr and Co, and the strong bonds with C and Al. We find Inconel740 has slightly stronger mechanical properties than Haynes282. Both Inconel740 and Haynes282 show ductile natures based on Poisson's ratio. Poisson's ratio shows marginal correlation with the TBOD. Comparison with more conventional high entropy alloys with equal components are discussed.
RESUMO
Chalcogenide crystals have a wide range of applications, especially as thermoelectric materials for energy conversion. Thermoelectric materials can be used to generate an electric current from a temperature gradient based on the Seebeck effect and based on the Peltier effect, and they can be used in cooling applications. Using first-principles calculations and semiclassical Boltzmann theory, we have computed the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, power factor, and figure of merit of 30 chalcogenide crystals. A Quantum Espresso package is used to calculate the electronic properties and locate the Fermi level. The transport properties are then calculated using the BoltzTraP code. The 30 crystals are divided into two groups. The first group has four crystals with quaternary composition (A2BCQ4) (A = Tl; B = Cd, Hg; C = Si, Ge, Sn; Q = S, Se, Te). The second group contains 26 crystals with the ternary composition (A'B'Q2) (A' = Ag, Cu, Au, Na; B' = B, Al, Ga, In; Q = S, Se, Te). Among these 30 chalcogenide crystals, the results for 11 crystals: Tl2CdGeSe4, Tl2CdSnSe4, Tl2HgSiSe4, Tl2HgSnS4, AuBSe2, AuBTe2, AuAlTe2, AuGaTe2, AuInTe2, AgAlSe2, and AgAlTe2 are revealed for the first time. In addition, temperature-dependent transport properties of pure and doped AgSbSe2 and AgSbTe2 crystals with dopant compositions of AgSb0.94Cd0.06Te2 and AgSbTe1.85Se0.15 were explored. These results provide an excellent database for bulk chalcogenides crucial for a wide range of potential applications in renewable energy fields.
RESUMO
Cement and concrete have been important construction materials throughout human history. There is an urgent need to explore novel and untraditional cementitious materials to enhance the durability of building materials and structures in response to increased infrastructure demand worldwide. We report an exploratory study on a biocomposite cement based on a large-scale computational study using density functional theory. An explicitly solvated mixture of a mineral calcium silicate hydrate (C-S-H) crystal suolunite (Ca2Si2O5(OH)2·H2O) and a silicon binding peptide with amino acid sequence PRO-PRO-PRO-TRP-LEU-PRO-TYR-MET-PRO-PRO-TRP-SER is constructed using ab initio molecular dynamics (AIMD). Detailed analysis on the interface structure, interatomic bonding, mechanical properties, and solvent effect of this model reveals a complex interplay of different types of covalent and ionic bonding, including ubiquitous hydrogen bonding which plays a crucial role in their properties. The use of the total bond order density (TBOD), a single quantum mechanical metric, for assessing the interfacial cohesion for this composite biocement is proposed. We find that the solvated model has a slightly larger TBOD than the dried one. These results could lead to a systematic search and rational design for different types of bioinspired and hybrid functional materials with other inorganic minerals and organic peptides.