  We expand upon the recent semi-stochastic adaptation to full configuration
interaction quantum Monte Carlo (FCIQMC). We present an alternate method for
generating the deterministic space without a priori knowledge of the wave
function and present stochastic efficiencies for a variety of both molecular
and lattice systems. The algorithmic details of an efficient semi-stochastic
implementation are presented, with particular consideration given to the effect
that the adaptation has on parallel performance in FCIQMC. We further
demonstrate the benefit for calculation of reduced density matrices in FCIQMC
through replica sampling, where the semi-stochastic adaptation seems to have
even larger efficiency gains. We then combine these ideas to produce explicitly
correlated corrected FCIQMC energies for the Beryllium dimer, for which
stochastic errors on the order of wavenumber accuracy are achievable.
