Optimizing the Computation of Many-Pair Density Matrix in VDPC

Recently an algorithm that acts the variational principle directly to a coherent-pair condensate (VDPC) has been proposed. This can avoid time-consuming projection while maintaining particle number conservation. Quickly computation of many-pair density matrix (MPDM) is one keys improve computational efficiency VDPC algorithm. In this work, we propose scheme limits energy range block particles vicinity Fermi surface, which reduces time complexity computing MPDM without losing physical details. The results show by appropriately limiting range, greatly reduce elements need be computed, and reducing required for computation.