Charge excitations in NaV2O5 - art. no. 075107

We calculate the electron-energy loss spectrum and the optical conductivity for NaV2O5 using the standard Lanczos algorithm. The vanadium ions in NaV2 O5 form a system of coupled ladders that can be described by a quarter-fill ed extended Hubbard model. Since this system has a large unit cell, one has to be very careful to avoid finite-size effects in the calculations. We sh ow this by performing exact diagonalization of different clusters with up t o 16 sites. The calculated loss function for the extended Hubbard model sho ws good agreement with experimental spectra. Furthermore, a qualitative des cription of the optical conductivity is obtained with the same Hamiltonian, and the same set of model parameters. The comparison with the experiment s hows that interladder hopping is of minor importance for a realistic descri ption of charge excitations in NaV2O5. We find that the character of the ex citations depends strongly on the direction of momentum transfer.