Berlin 2005 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 31: Polymer physics: special techniques
CPP 31.3: Talk
Wednesday, March 9, 2005, 10:15–10:30, TU C130
Exact cutoff techniques in supercell calculations — •Carlo Andrea Rozzi1, Angel Rubio2, and Eberhard K.U. Gross1 — 1Freie Universität Berlin — 2Donostia International Physics Center (DIPC)
TDDFT has been shown to be an excellent approach to correctly and efficiently describe excited states in atoms and molecules. Yet, when applied to infinite periodic systems, both conceptual and implementational problems arise. Among them the question whether or not it is possible to describe a bound exciton in infinite periodic systems using pure TDDFT is still not completely answered. This problem is particularly challenging in systems that are periodic in less than three dimensions, like polymers and nanotubes (1D periodic), or surfaces and thin films (2D periodic). Such systems are usually treated in a supercell approach, as a three dimensional array of chains or slabs, and the computational cost for the simulations dramatically increases with the cell size. Moreover, due to the long range character of the Coulomb interaction, the equivalent isolated system (i.e. the single chain or film) is exactly described only in the limit of an infinite supercell. This has lead to the request for efficient techniques to cut off the Coulomb interaction in systems with reduced periodic dimensionality. We will show how to calculate exact analytical cutoffs to properly screen at a desired extent the long range Coulomb interaction in both 1D and 2D systems. This allows one to compute most efficiently the properties of the infinite system alone to compare them with those of the system plus its periodic images.