Some improvements of the activation-relaxation technique method for finding transition pathways on potential energy surfaces.

The activation-relaxation technique nouveau is an eigenvector following method for systematic search of saddle points and transition pathways on a given potential energy surface. We propose a variation in this method aiming at improving the efficiency of the local convergence close to the saddle point. The efficiency of the method is demonstrated in the case of point defects in body centered cubic iron. We also prove the convergence and robustness of a simplified version of this new algorithm.

Nonlinear instability of density-independent orbital-free kinetic-energy functionals.

We study in this article the mathematical properties of a class of orbital-free kinetic-energy functionals. We prove that these models are linearly stable but nonlinearly unstable, in the sense that the corresponding kinetic-energy functionals are not bounded from below. As a matter of illustration, we provide an example of an electronic density of simple shape, the kinetic energy of which is negative.

Maximal probability domains in linear molecules.

Regions of space are defined to maximize the probability to find a given number of electrons within. Their chemical significance and their relationship to the electron localization function (ELF) are explored by analyzing the results for a few linear molecules: LiH, BH, N2, CO, CS, C2H2, and C4H2.