The coordinates of the systems are shown in the Supporting Information. After obtaining the relationship between the number of walkers and the minimum matching error that it can achieve, one can then plot to obtain an expression of the form log(y) = a+b×log(x), in which x is the number of walkers and y is the matching error. This is naturally justified, as using an infinite number of walkers can, in theory, reduce the matching error to zero and work just like a deterministic FCI calculation. The Hilbert space sizes of individual fragments and the fitted parameters of the equations between the number of walkers and the matching error for the investigated systems are shown in Table below. Excellent agreement can be seen from the fact that every R 2 value in the plot for all of the eight systems investigated is greater or equal to 0.95, although it should be noted that these parameters are approximate due to the stochastic nature of BE-i-FCIQMC. Several observations can be concluded from the table, which will be outlined below. According to the table, regardless of the sign of parameter a, the sign of parameter b is always negative. This means that the magnitude of matching error decreases monotonically with the number of walkers. This can be explained by an increase in the quality of the function and the decrease of the initiator error that is caused by selected generation of particles, which is true regardless of what the system is.