Eur. Phys. J. B 6, 213-223 (1998)
https://doi.org/10.1007/s100510050544

Optimal coupled-cluster approximation for the ground-state properties of a spin-boson model

Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong

Corresponding author: ^a cflo@phy.cuhk.edu.hk

Received: 11 March 1998
Accepted: 23 June 1998
Published online: 15 November 1998

Abstract

In the present work we have developed an optimal coupled-cluster approximation, which can take care of both the accuracies of the ground-state energy and the wavefunction estimates, for the ground state of a two-state system coupled to a dispersionless boson bath. This new approach is also able to give a tight upper bound to the ground-state energy of the system. Up to the fourth level of this approximation our results show excellent agreement with the numerical exact diagonalization results. In particular, our results suggest no discontinuous localization-delocalization transition of the two-state system. This is consistent with the exact result.