Dr. Carlo Andrea Rozzi

During last year I have been addressing the question whether it is possible to correctly describe a bound exciton in infinite periodic systems using TDDFT. In order to answer to this question I first started to extend the field of applicability of a real space, real time TDDFT code (octopus), that was originally designed for finite systems. The main point in doing this is the possibility to apply the real time propagation methods already implemented in the code to a case where the existence of solid state excitations makes the many body calculations particularly complicated. Even if the first natural application to the real world is the calculation of optical absorption spectra in polymers, I tried to implement the changes in such a way that it is also possible to describe also traditional solids as well as surfaces (i.e. 2d infinite systems). In order to do this we have to treat the system as finite in the non periodic directions, that means introducing appropriate cutoff technique for the ionic and Hartree potentials. I worked out and implemented such cutoffs in the code, together with the pure 3D periodic machinery. In the second part of the project I am going to move to the truly time dependent part of the problem for the periodic dimensions.

Exchange visits and workshops attended:
International conference on Nanoelectronics, Lancaster, 4-9 Jan 2003
Exciting Summer school 2003, Riksgraensen (SE), 22-30 June 2003
Mini workshop on real-space methods in electronic structure calculations, CSC, Finnish IT Center for Science, Helsinki, 7-8 Aug 2003
Workshop on ab initio electrons excitations theory: towards systems of biological interest, DIPC, San Sebastian/Donostia, 21-24 Sep 2003
FHI - FU Workshop, Stralsund (Germany) 25-27 Sep 2003
Visits to DIPC, San Sebastian/Donostia, c/o Prof. A. Rubio, 24 May - 20 Jun 2003, and 5-19 Dec 2003.

New features implemented in OCTOPUS are periodic boundary conditions in arbitrary directions; k-point weighted sums in calculation of densities; the generation of k-points grid by Monkhorts-Pack; a symmetry-driven reduction of the Brillouin zone; the symmetrization of the density in periodic directions; the calculation of potentials in periodic directions; 1D, 2D, 3D cutoffs in non-periodic directions for local and Hartree potentials.