Effective valence-bond theory for strongly correlated systems

Abstract : The present paper describes how to extract accurate effective Valence-Bond models for strongly correlated compounds. It details how, in difficult cases, it is possible to choose the model space supporting the effective Hamiltonian using a joint diagonalization of the target states density matrices. The information is reduced from the target MRCI states to the effective model using the effective Hamiltonians concepts. The problems of non-orthogonality and accuracy are discussed. The methodology is briefly illustrated by a couple of examples of applications.