Dynamic Correlations and the Ground State of MnSi

MnSi is a metallic helimagnet below 29 K. Above 1.46 GPa, the moment is completely suppressed resulting in an unusual magnetic state. Density functional theory (DFT) predicts that MnSi has a moment of 1.0 $\mu_B$/Mn, which is much larger than the measured value of $\sim$0.4 4$\mu_B$/Mn. Additionally, DFT predicts a smaller magnetovolume coupling than found in experiment. We found that the addition of a Hubbard-U reproduces the experimental moment, but worsens the pressure dependence. We explored the effect of dynamic correlations on the pressure dependence of the moment using a fluctuating exchange approximation (FLEX), and contrast our results for MnSi with the B20 form of FeGe, which exhibits similar behaviors.