Abstract

Pressure-induced changes in the magnetic and superconducting properties of the odd-parity superconductor candidate UTe2 have attracted considerable interest, underscoring the need for microscopic theoretical insight. In this study, we investigate the electronic structure and magnetic fluctuations at ambient pressure and under pressure using density functional theory (DFT) combined with the random phase approximation (RPA). For each pressure, we perform DFT+U calculations for several values of the Coulomb interaction U, construct a 72-orbital periodic Anderson model, and calculate magnetic susceptibilities within the RPA framework. For U = 2 eV, the Fermi surface has a quasi-two-dimensional shape, and antiferromagnetic fluctuations develop with a wave vector Q1 || a*, accompanied by magnetic anisotropy χ^b > χ^a > χ^c. Under pressure, the antiferromagnetic fluctuations are suppressed due to a reduced density of states at the Fermi level, and the magnetic anisotropy is weakened. In contrast, for U = 1 eV, antiferromagnetic fluctuations with Q2 || b* appear, accompanied by anisotropy χ^a > χ^c > χ^b, consistent with experiments. Under pressure, the antiferromagnetic fluctuations around Q2 are enhanced, the magnetic wave vector tilts slightly toward the a* direction due to Fermi-surface distortion, and the magnetic anisotropy is suppressed. These results demonstrate that the pressure evolution of magnetism in UTe2 is governed by the momentum-space distribution of U 5f states and the density of states at the Fermi level, providing a microscopic basis for understanding its magnetic and superconducting properties.