Spin-density fluctuations and the energy of liquidHe3

We introduce spin-density fluctuations into the Slater-Jastrow trial wave function for liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ using a spin-dependent correlation operator. The unpolarized ground-state energy is thereby lowered by 0.3 K and probably stabilized with respect to the polarized state. A crucial element in the calculation is the correct treatment of a substantial cancellation between direct and exchange contributions to the energy.