Density Matrix Embedding Theory (DMET) is a theoretical framework used to treat finite fragments in the presence of a surrounding molecular or bulk environment, especially when there is significant correlation or entanglement between the two [[1](https://arxiv.org/abs/1603.08443)]. This theory is a type of [[Fragmentation Strategies]] used in quantum chemistry and physics to handle complex systems by breaking them down into smaller, more manageable parts, or fragments. DMET explicitly allows for **quantum entanglement between the system and its environment, which sets it apart from most embedding methods** [[2](https://arxiv.org/abs/1605.05547)]. This is particularly important in the study of strongly correlated systems, where interactions between particles play a crucial role. In summary, DMET is a powerful tool in quantum chemistry and physics that allows for the study of complex systems by breaking them down into smaller parts and considering the interactions between these parts and their environment. This approach has been extended and combined with other methods to improve its efficiency and applicability to a wide range of problems.