Thermodynamics of tetravalent thorium and uranium complexes from first-principles calculations.

Enthalpies of formation for the ThX4 and UX4 (X = F, Cl, OH) species have been investigated with density functional theory and coupled-cluster methods. ThX4 molecules are all confirmed as tetrahedral, while all UX4 molecules are predicted to adopt D2d symmetry using density functional theory. Multireference coupled cluster approaches confirm the D2d symmetry for UF4.

Structure and hydrolysis of the U(IV), U(V), and U(VI) aqua ions from ab initio molecular simulations.

Ab initio molecular dynamics simulations at 300 K, based on density functional theory, are performed to study the hydration shell geometries, solvent dipole, and first hydrolysis reaction of the uranium(IV) (U(4+)) and uranyl(V) (UO(2)(+)) ions in aqueous solution. The solvent dipole and first hydrolysis reaction of aqueous uranyl(VI) (UO(2)(2+)) are also probed. The first shell of U(4+) is coordinated by 8-9 water ligands, with an average U-O distance of 2.

Bonding and adhesion at the SiC/Fe interface.

Ceramics such as SiC have the potential to act as protective coatings, primarily due to their high melting points and wear resistance. We use periodic density functional theory (DFT) within the generalized gradient approximation (GGA) to calculate the adhesion strength between SiC and Fe, for Si- and C-terminations of SiC(100) and two surfaces of Fe: (100) and (110). We predict a maximum ideal work of adhesion of 6.

Nonadiabaticity in the iron bcc to hcp phase transformation.

Iron is known to undergo a pressure-induced phase transition from the ferromagnetic (FM) body-centered-cubic (bcc) alpha-phase to the nonmagnetic (NM) hexagonal-close-packed (hcp) epsilon-phase, with a large observed pressure hysteresis whose origin is still a matter of debate. Long ago, Burgers [Physica (Amsterdam) 1, 561 (1934)] proposed an adiabatic pathway for bcc to hcp transitions involving crystal shear followed by atom shuffles. However, a quantum mechanics search in six-dimensional stress-strain space reveals a much lower energy path, where the crystal smoothly shears along the entire path while the atoms shuffle only near the transition state (TS).