Excess electron states in fluid methane: Density-functional versus Lanczos approaches

Abstract We compare density-functional theory (DFT) electronic structure calculations at the hybrid B3LYP level for fluid methane with experiments and a pseudo-potential Lanczos method. We generate fluid configurations from classical/ ab initio molecular dynamics and use DFT to determine one-particle orbital and total energies. Our results show that DFT predicts excess electron energies that qualitatively agree with experiments over a density range, provided these values are determined from total energy differences between charged and neutral systems. By contrast, orbital energies of the lowest unoccupied state of the N -electron system provide qualitatively incorrect excess electron energies as a function of the fluid density.