First-principles structural optimization and electronic structure of the superconductor picene for various potassium doping levels

TL;DR

This study uses first-principles calculations to analyze the structural and electronic properties of potassium-doped picene across various doping levels, revealing complex structural arrangements and diverse electronic behaviors relevant to superconductivity.

Contribution

It provides a comprehensive first-principles analysis of K$_x$picene structures and electronic properties for $x=1$-4, highlighting multiple stable configurations and the invalidity of the rigid-band approximation.

Findings

Multiple stable structures exist for certain doping levels.

Dopants can enter both interlayer and intralayer regions.

Fermi surface topology varies significantly with doping level.

Abstract

We theoretically explore the crystal structures of K$_x$picene, for which a new aromatic superconductivity has recently been discovered for $x=3$, by systematically performing first-principles full structural optimization covering the concentration range $x=1$-4. The crystal symmetry (space group) of the pristine picene is shown to be preserved in all the optimized structures despite significant deformations of each picene molecule and vast rearrangements of herringbone array of molecules. For K$_x$picene ($x=1$-4) optimization indicates that (i) multiple structures exist in some cases, and (ii) dopants can enter not only in the interlayer region between the stack of herringbone structures, but also in the intralayer region. In the electronic structure obtained with the local density approximation for the optimized structures, the dopants are shown to affect the electronic properties not only through the rearrangement and distortion of molecules, but also molecule-metal atom hybridization. In other words, the rigid-band approximation is invalidated for multifold reasons. As a consequence the resultant Fermi surface exhibits a variety of multiband structures which take diverse topology for K$_1$picene and K$_3$picene.