Available on-demand - F.NM06.10.02
First Principles Calculation of the Electronic Structure of V(TCNE)2
Yueguang Shi1,Michael Flatté1
The University of Iowa1
Over the past two decades there has been growing interest in organic magnetic materials, due to their potential applications in the field of magnonics and spintronics.[1,2,3,4] Vanadium tetracyanoethylene, V(TCNE)x≈2, is a room temperature ferrimagnetic semiconductor with a Tc ~ 600 K  which has very low loss ferromagnetic resonance and spin-wave propagation[1, 2]. Previous first principles calculations of the electronic structure have indicated a substantially larger band gap (0.8 eV) than experimentally inferred (0.5 eV) [6,7], and that the band gap itself is an indirect gap with the valence maximum located at the (0,0,0.5) point and the conduction minimum at the (0,0.5,0) point. Our crystal axes are defined so that an equatorial TCNE ligand lies in the plane (0 0 1) and an apical ligand lies in (1 1 0) in a unit cell. The study of Ref. 6 used a local-orbital calculation with B3LYP hybrid functional. Here we explore the electronic structure using a plane-wave code VASP[8,9,10]. We have tried the following functionals: Perdew-Burke-Ernzerhof (PBE), PBE0, Becke, 3-parameter, Lee-Yang-Parr (B3LYP), Heyd-Scuseria-Ernzerhof (HSE06). The ferrimagnetic structure is studied using both collinear magnetic structure calculations and non-collinear calculations. We confirm that the structure of VTCNE has a triclinic unit cell with each V atom surrounded by 6 organic ligands, as found in Ref. 6. However, in contrast to the previous study we find a direct band gap of 0.4 eV located at the (0,0.5,0.5) point. This band gap better agrees with the experimental inference from the conductivity activation energy . Further studies will explore the optical properties of this material and its magnetic dynamics, including anisotropy and magnetoelastic properties.
We acknowledge funding from NSF Grant No. DMR-1808742.
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