An optimized cluster density matrix embedding theory

We propose an optimized cluster density matrix embedding theory (CDMET). It reduces the computational cost of CDMET with simpler bath states. And the result is as accurate as the original one. As a demonstration, we study the distant correlations of the Heisenberg J₁-J₂ model on the square lattice. We find that the intermediate phase (0.43≤sssim J₂≤sssim 0.62) is divided into two parts. One part is a near-critical region (0.43≤J₂≤0.50). The other part is the plaquette valence bond solid (PVB) state (0.51≤J₂≤0.62). The spin correlations decay exponentially as a function of distance in the PVB.