they cannot be compared one-to-one, however by observing the error with respect to FCI and the number of determinants used in Fig. , general trends can be observed. The HCI and RLCI methods are competitive in the sense that both methods can be tuned to yield errors below chemical accuracy with reasonable wave function compression (worst case for all methods for N 2 here are still < 10% of the total FCI space). As can be seen, in order to get the accuracies to roughly agree in Fig. , the number of parameters (determinants)