Backflow transformation improves QMC calculations of silicon self-interstitial defects

Recent advances in quantum Monte Carlo (QMC) reduce error introduced by approximations. Direct improvement of the trial wave function through backflow transformation of the electron coordinates[1] produces a wave function closer to the ground state by moving electrons out of the way of a given electron. Adding plane waves of particle position to the Jastrow factor[2] augments the accounting for interparticle correlation in QMC calculations by capturing the ``corners'' of the simulation cell neglected when the Jastrow is only a function of pair separation. Hybrid density functionals have produced better starting trial wave functions for molecules by incorporating some exact exchange to more accurately describe electron-electron interactions. We apply backflow transformation, plane-wave-expanded Jastrow factors and hybrid functional trial wave functions to QMC calculations of silicon self-interstitial defects. [1] L\'opez-R\'ios {\it et al.}, Phys. Rev. E {\bf 74}, 066701 (2006). [2] Drummond {\it et al.}, Phys. Rev. B {\bf 70}, 235119 (2004).