# Events

**Date:**12.12.2011

**Time:**4:30 p.m.

**Place:**UHW 11/1102

*Volker Blum*, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

Quantum-mechanical first principles (e.g., density-functional theory) provide us with

an enormously successful, essentially accurate computational framework for the

potential energy surface that governs materials or molecular properties, chemical

reactions etc. One of the ongoing challenges is that we can reach benchmark-level

accuracy for small systems (few-atom molecules) relatively easily, but pushing the

same benchmark accuracy out to large systems -- when it matters – is an ongoing

challenge.

This talk focuses on two areas where high accuracy for relatively large structure

sizes (hundreds or thousands of atoms) is indeed desirable, if it can be had: (i) The

structure, stability and dynamics in biomolecular systems, where relatively weak

interactions (e.g., Hydrogen bonds, van der Waals) make a critical difference, and

(ii) surface reconstruction at a larger scale, where the physically relevant structure

of an interface is determined by relatively small (per atom) energy contributions.

We use all-electron electronic structure theory as implemented in the FHI-aims code

to meet these challenges. Numeric atom-centered basis sets provide essentially

converged numerical accuracy for the task at hand, and efficient parallelization up

to massively parallel architectures (hundreds or thousands of processors) allows us

to reach the relevant system sizes. In particular, we address the possible bottleneck

of an algebraic eigenvalue solver (Kohn-Sham equations) on massively parallel

machines. On the biomolecular side, we focus on polyalanine molecules (5-20

aminoacids) large enough to form secondary or tertiary structure, where accurate

vacuum experiments (IR spectroscopy) are available for quantitative comparisons to

experiment. Regarding surface reconstruction, we address the structure and

thermodynamic stability of commensurate, graphene-like

reconstructions that form on SiC(111).