Realistic Description of TTF-TCNQ - a Strongly Correlated Organic Metal

Understanding the physics of strongly correlated materials is one of the grand challenges in condensed-matter physics. Simple approximations such as the local density approximation fail, due to the importance of the Coulomb repulsion between localized electrons. Instead we have to resort to non-perturbative many-body techniques. Such calculations are, however, only fea- sible for quite small model systems. This means that the full Hamiltonian of a real material has to be approximated by a model Hamiltonian comprising only the most important electronic degrees of freedom, while the effect of all other electrons c an merely be included in an aver- age way in form of parameters. In this work we describe how to calculate those parameters for the one-dimensional organic metal TTF-TCNQ. Having constructed the Hamiltonian we calculate the ground state and dynamical properties with the Lanczos method. This method is limited by the available main memory. We show how to make efficient use of the memory and computational power of the massively parallel BlueGene/L system for such calculations. To gain high-resolution angular-resolved spectral function s we employ cluster perturbation theory (CPT) which helps identifying signatures of spin-charge separation also found experimentally in TTF-TCNQ. Increasing the nearest neighbour interaction is studied using a periodic version of CPT (kCPT).