Figure : result of the computational time of the double-precision method and the mixed-precision scheme. This is the time for the entire DMRG calculation, instead of the time for one sweep. The corresponding speed-up for each test is attached on top of the bar of the mixed-precision scheme. (*): Note that only mixed-diagonalization method was applied for chromium dimer system. This is because when transition metal elements are involved, the performance of the single-precision sweep will be slower than the mixed-diagonalization optimized double-precision sweep.