1. From a given reference, initialize the set s through the greedy probing algorithm proposed in Ref 48. In this work, we use the HF wave function as the reference. Briefly, the greedy probing method builds up the set s incrementally through a perturbation-based approach until dim(s) = k, at which the procedure terminates. The new determinants to be added to s are obtained from the first-order perturbative wave function estimate, as is commonly used in other sCI methods, such as CIPSI and ASCI