Inhomogeneous backflow transformations in quantum Monte Carlo   calculations
  An inhomogeneous backflow transformation for many-particle wave functions is presented and applied to electrons in atoms, molecules, and solids. We report variational and diffusion quantum Monte Carlo VMC and DMC energies for various systems and study the computational cost of using backflow wave functions. We find that inhomogeneous backflow transformations can provide a substantial increase in the amount of correlation energy retrieved within VMC and DMC calculations. The backflow transformations significantly improve the wave functions and their nodal surfaces. 
P. Lopez-Rios, A. Ma, N. D. Drummond, M. D. Towler, and R. J. Needs