Characterization of the Fermi surface of BEDT-TTF$_4$[ Hg$_2$Cl$_6$] .PhCl by electronic band structure calculations

Tight-binding band structure calculations for the room temperature structure of BEDT-TTF$_4$[ Hg$_2$Cl$_6$] .PhCl show the existence of closed electron and hole Fermi surfaces, in agreement with the 2D metallic conductivity of this salt. It is shown that these closed Fermi surfaces result from the hybridization of two hidden 1D Fermi surfaces. However, our study also shows that a transition associated with either a usual or a hidden nesting type mechanism is unlikely. This explains why this salt retains its metallic properties without any resistivity anomaly down to 1.3 K. Our study suggests that BEDT-TTF$_4$[ Hg$_2$Cl$_6$] .PhCl is a somewhat anisotropic 2D semimetal and should exhibit Shubnikov-de Haas oscillations corresponding to a cross-sectional area of approximately 13 % of the first Brillouin zone