Luiz A. C. Malbouisson

Carbon in copper and silver: Diffusion and mechanical properties

Abstract The effects of interstitial carbon on the diffusion and mechanical properties of copper and silver are studied theoretically. Semiempirical methodology, atomistic simulations, and first-principles density functional schemes are combined to extract some understanding of the diffusion process and lattice reconstruction in extremely dilute interstitial Cu–C and Ag–C alloys. It is demonstrated that carbon inclusion in the host matrix leads to sufficient non-uniform dilatation of the lattice. We also show that an account of static displacements is important in the calculations of the activation energy for the diffusion of the interstitial atoms. The “embedded” cluster scheme is suggested to simulate the relaxation in extremely dilute alloys. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu–C interface.

Diffusion properties of tungsten from atomistic simulations with ab initio potentials

Abstract The results of atomistic simulations of migration and formation energies of mono- and di-vacancies in bulk tungsten are presented in our paper. The interatomic potential for tungsten was extracted with the recursive procedure from ab initio calculations of the cohesive energy. A stochastic molecular dynamics using a generalized simulated annealing procedure was employed in the simulations. Calculated values of mono- and di-vacancies energy parameters are in a good agreement with experimental data and with the results of other calculations.

Non-linearity of the Hartree-Fock equations. Multiple Hartree-Fock solutions.

We determined multiple closed-shell Hartree-Fock-Roothaan solutions for the systems: BH, FH, LiH, and OH−, considering double and triple zeta bases. To calculate them, we used the self-consistent field method and the algebraic method. The Hartree-Fock solutions obtained were classified with respect to the kind of extreme. All these extremes generate the same configuration interaction space. Our key objective in this work is to illustrate that it is possible to obtain a wide variety of Hartree-Fock solutions for any molecular system.