Large scsle quantum simulations: C60 Impacts on a semiconducting surface

First principles molecular dynamics calculations of the mechanical properties of endofullerenes containing noble gas atoms or small molecules

The mechanical properties of endofullerenes have been investigated by performing compression tests using finite temperature first principles molecular dynamics calculations. We considered various X@C₆₀ systems, with X a single noble gas atom (He, Ne, Ar, Kr, or Xe), small molecules (H₂O, CH₄), or small helium clusters. In the absence of compression, it is observed that there is no or at best a negligible effect of X on the properties of C₆₀. The compression simulations revealed several original findings. First, the influence of X on the stiffness of X@C₆₀ can be quantified, although it is at most 12% for the studied cases. Next, both energy and contact force variations as a function of strain are demonstrated to depend on X. However, this is not the case for the yield strain and for the failure mechanism of the C₆₀ shell. Finally, it is shown that the X@C₆₀ compression could bring X to be in a high stress state. In the specific cases of H₂O and CH₄ molecules, a mechanism of stress assisted dissociation is observed.

O(N) methods in electronic structure calculations

Linear-scaling methods, or O(N) methods, have computational and memory requirements which scale linearly with the number of atoms in the system, N, in contrast to standard approaches which scale with the cube of the number of atoms. These methods, which rely on the short-ranged nature of electronic structure, will allow accurate, ab initio simulations of systems of unprecedented size. The theory behind the locality of electronic structure is described and related to physical properties of systems to be modelled, along with a survey of recent developments in real-space methods which are important for efficient use of high-performance computers. The linear-scaling methods proposed to date can be divided into seven different areas, and the applicability, efficiency and advantages of the methods proposed in these areas are then discussed. The applications of linear-scaling methods, as well as the implementations available as computer programs, are considered. Finally, the prospects for and the challenges facing linear-scaling methods are discussed.