Basis Optimization Renormalization Group for Quantum Hamiltonian

A method of Hamiltonian diagonalization is suitable for calculating physical quantities associated with wavefunctions, such as structure functions and form factors. However, we cannot diagonalize Hamiltonian directly in quantum field theories because dimension of Hilbert space is generally infinite. To create effective Hamiltonian, we extend a technique of NRG (numerical renormalization group) proposed by K. Wilson [1]. In spin chain models, any state can be expanded with a direct product of two sets of basis states, each of which is for one of two spin blocks. For a finite lattice, we can calculate wavefunction Ψij of the ground state by diagonalizing Hamiltonian. In Ref. [2], S.White has found that singular values Dk of target-state wavefunction Ψij = ∑