Crystal Structures and Electronic Properties of Haloform-Intercalated C60

TL;DR

This study uses density functional theory to analyze the structural and electronic properties of haloform-intercalated C60 compounds, revealing their insulating nature, orbital interactions, charge distribution, and sensitivity of electronic states to molecular orientation.

Contribution

It provides detailed computational insights into the electronic structure and charge distribution of haloform-intercalated C60, highlighting effects of molecular orientation and intercalation on electronic properties.

Findings

Both compounds are narrow band insulators with gaps >1 eV.

Charge is partially delocalized onto haloform molecules.

Density of states at Fermi energy varies with molecular orientation.

Abstract

Using density functional methods we calculated structural and electronic properties of bulk chloroform and bromoform intercalated C60, C60 2CHX3 (X=Cl,Br). Both compounds are narrow band insulator materials with a gap between valence and conduction bands larger than 1 eV. The calculated widths of the valence and conduction bands are 0.4-0.6 eV and 0.3-0.4 eV, respectively. The orbitals of the haloform molecules overlap with the $\pi$ orbitals of the fullerene molecules and the p-type orbitals of halogen atoms significantly contribute to the valence and conduction bands of C60 2CHX3. Charging with electrons and holes turns the systems to metals. Contrary to expectation, 10 to 20 % of the charge is on the haloform molecules and is thus not completely localized on the fullerene molecules. Calculations on different crystal structures of C60 2CHCl3 and C60 2CHBr3 revealed that the density of states at the Fermi energy are sensitive to the orientation of the haloform and C60 molecules. At a charging of three holes, which corresponds to the superconducting phase of pure C60 and C60 2CHX3, the calculated density of states (DOS) at the Fermi energy increases in the sequence DOS(C60) < DOS(C60 2CHCl3) < DOS(C60 2CHBr3).