Normal state of metal-intercalated phenacene crystals: Role of electron   correlations
  In this work we study the effect of long range electron-electron correlations on the behavior of the normal state of metal-intercalated phenacene crystals. While the individual phenacene molecules are modeled by the Pariser-Parr-Pople Hamiltonian with long range Coulomb interactions, we derive a correlated minimal model for describing the phenacene ionic crystals. We find that long range electron correlations do not change the behavior of the phenacene ions with molecular valence $-1$ (monoanion) and $-2$ (dianion), compared to that observed for short range electron interactions. The monoanion crystal is a single-band $\frac{1}{2}$-filled antiferromagnetic Mott-Hubbard semiconductor while the dianion crystal is a two-band semiconductor with inter-molecular antiferromagnetic and intra-molecular ferromagnetic spin orderings. However, the trianion crystal is no longer a nearly degenerate $\frac{3}{4}$-filled two-band system. We show that this occurs because the kinetic stability of the $\frac{3}{4}$-filled two-band system with long range correlations is smaller compared to that with short range correlations, for the lattice sizes considered in this study. We argue that with large finite lattices, behavior of the trianion crystal with long range correlations will be same as that with short range correlations. We thus conclude that long range correlations fail to alter the normal states of metal-intercalated phenacene crystals. 
Tirthankar Dutta and Sumit Mazumdar
cond-mat.str-el cond-mat.supr-con