T expansion: A nonperturbative analytic tool for Hamiltonian systems

摘要: A systematic nonperturbative scheme is developed to calculate the ground-state expectation values of arbitrary operators for any Hamiltonian system. Quantities computed in this way converge rapidly their true values. The method based upon use operator e/sup -t/H contract trial state onto ground H. We express all contracted as a power series t, and reconstruct t..-->..infinity behavior by means Pade approximants. problem associated with factors spatial volume taken care developing connected graph expansion matrix elements between states. investigate methods t discuss merits various procedures. As examples technique we present results obtained Heisenberg Ising models 1+1 dimensions starting from simple mean-field wave functions. improvement remarkable amount effort required. connection our conventional perturbation theory established, generalization which allows us exploit off-diagonal introduced. bistate procedure used develop tmore » energy model is, term term, self-dual.« less