The FCIQMC wave function is propagated along the imaginary time, τ , in discretized steps, ∆τ . The iterative procedure of the FCIQMC dynamics consists of four main stages: excitation generation, spawn, death, and annihilation. In the excitation generation stage, new configurations |D j are suggested as targets. In the spawn step, new walkers are then spawned to |D j from |D i (i = j), with a probability p spawn ∝ ∆τ D i | Ĥ | D j . In the death step, configurations |D i are killed with a probability proportional to their diagonal matrix element ∝ ∆τ D i | H | D i . In the annihilation step, walker contributions (arising from different spawning events) residing on the same configuration are summed up with their respective signs. If they are of identical amplitude and opposite sign, they annihilate each other and any information about that configuration is removed from the data tables.