Electronic structure and Fermi surface of paramagnetic and antiferromagnetic UPt2Si2

Abstract

We report density functional theory-based calculations of the electronic structure and Fermi surface properties of the intermetallic uranium compound UPt${}_{2}$Si${}_{2}$, which orders antiferromagnetically at ${T}_{N}=32$ K with a total magnetic moment of 2${\ensuremath{\mu}}_{B}$/U-atom and exhibits a moderate mass enhancement in the specific-heat coefficient. Our investigation is carried out using relativistic, full-potential band-structure methods within the framework of the local spin density approximation (LSDA), the LSDA with orbital polarization correction (LSDA+OPC), and the LSDA supplemented with an additional Hubbard $U$ (LSDA+$U$). We find that the LSDA+OPC scheme predicts the total magnetic moment in best agreement with experiment; from this we infer that the $5f$ electrons in UPt${}_{2}$Si${}_{2}$ are orbitally polarized, mostly itinerant, and exhibit only a slight tendency toward localization. Our total energy calculations predict UPt${}_{2}$Si${}_{2}$ to form in the CaBe${}_{2}$Si${}_{2}$ ($P4/nmm$) structure, in contrast to URu${}_{2}$Si${}_{2}$ (ThCr${}_{2}$Si${}_{2}$: $I4/mmm$). The theoretical Fermi surfaces are also studied for the nonmagnetic and antiferromagnetic phases with the employed computational schemes and are found to be quasi-two-dimensional. At the antiferromagnetic transition, the Fermi surface is found to become more two-dimensional with small regions of gapping.