As shown in Figure , the logarithm of computational times for CASCI and CASPT2 calculations decreased almost linearly with the logarithm of the core number, except for anomalies observed in the 16-core and 64-core CASCI calculations, as well as the 64-core CASPT2 calculations. Due to the relatively small size of the CAS in this test, constructing matrix elements from 1e and 2e integrals consumes more computational time than matrix algebra operations such as diagonalization. This led to high parallelization efficiencies, e.g., 77% and 96% for 32-core CASCI and CASPT2 calculations, respectively, as the construction of matrix elements can be effectively parallelized. The anomaly of 16-core computational times in CASCI were not observed when we used a different single-node computer equipped with 48 cores, indicating that these anomalies do not always happen because of the structure of our program (see Figure in the supporting information (SI)).