Quantum Monte Carlo simulations using Slater-Jastrow-backflow wave function

Diffusion Quantum Monte-Carlo computations of the ground state energies of the Li, Li-, Be, Be+, B and B+ species are reported. We use trial wave function of four types: single determinant Slater-Jastrow, single determinant Slater-Jastrow-Backflow, multi-determinant Slater-Jastrow and multi-determinant Slater-Jastrow-Backflow. The single determinant wave functions are computed by the HF method and the multi-determinant wave functions are computed by the CI and CASSCF methods. Up to 99.9% and 100% of the correlation energy are recovered for the studied species without and with the backflow transformation respectively.