Bulik, Ireneusz W.Scuseria, Gustavo E.Dukelsky, Jorge2016-01-292016-01-292014Bulik, Ireneusz W., Scuseria, Gustavo E. and Dukelsky, Jorge. "Density matrix embedding from broken symmetry lattice mean fields." <i>Physical Review B,</i> 89, no. 3 (2014) American Physical Society: 035140. http://dx.doi.org/10.1103/PhysRevB.89.035140.https://hdl.handle.net/1911/88275Several variants of the recently proposed density matrix embedding theory (DMET) [G. Knizia and G. K-L. Chan, Phys. Rev. Lett. 109, 186404 (2012)] are formulated and tested. We show that spin symmetry breaking of the lattice mean-field allows precise control of the lattice and fragment filling while providing very good agreement between predicted properties and exact results. We present a rigorous proof that at convergence this method is guaranteed to preserve lattice and fragment filling. Differences arising from fitting the fragment one-particle density matrix alone versus fitting fragment plus bath are scrutinized. We argue that it is important to restrict the density matrix fitting to solely the fragment. Furthermore, in the proposed broken symmetry formalism, it is possible to substantially simplify the embedding procedure without sacrificing its accuracy by resorting to density instead of density matrix fitting. This simplified density embedding theory (DET) greatly improves the convergence properties of the algorithm.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlehttp://dx.doi.org/10.1103/PhysRevB.89.035140