Optimizing momentum space DMRG using quantum information entropy

摘要

In order to optimize the ordering of the lattice sites in the momentum spaceand quantum chemistry versions of the density matrix renormalization group(DMRG) method we have studied the separability and entanglement of the targetstate for the 1-D Hubbard model and various molecules. By analyzing thebehavior of von Neumann and Neumann-Renyi entropies we have found criteria thathelp to fasten convergence. A new initialization procedure has been developedwhich maximizes the Kullback-Leibler entropy and extends the active space (AS)in a dynamical fashion. The dynamically extended active space (DEAS) procedurereduces significantly the effective system size during the first half sweep andaccelerates the speed of convergence of momentum space DMRG and quantumchemistry DMRG to a great extent. The effect of lattice site ordering on thenumber of block states to be kept during the RG procedure is also investigated.