We present a detailed study of the derivation of the Hubbard model parameters for $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ in the framework of { \it ab initio} Density Functional Theory. We show that calculations with different (i) wavefunction basis, (ii) exchange correlation functionals and (iii) tight-binding models provide a reliable benchmark for the parameter values. We compare our results with available extended H\"uckel molecular orbital calculations and discuss its implications for the description of the properties of $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$. The electronic properties of $\kappa$-(ET)$_2$Cu(SCN)$_2$ are also briefly discussed.
Categories: cond-mat.str-el