Fixed-Node Monte Carlo Calculations for the 1d Kondo Lattice Model

van Bemmel, H. J. M.; van Saarloos, W.; Haaf, D. F. B. ten

Fixed-Node Monte Carlo Calculations for the 1d Kondo Lattice Model

Authors

van Bemmel, H. J. M.

van Saarloos, W.

Haaf, D. F. B. ten

Description

The effectiveness of the recently developed Fixed-Node Quantum Monte Carlo method for lattice fermions, developed by van Leeuwen and co-workers, is tested by applying it to the 1D Kondo lattice, an example of a one-dimensional model with a sign problem. The principles of this method and its implementation for the Kondo Lattice Model are discussed in detail. We compare the fixed-node upper bound for the ground state energy at half filling with exact-diagonalization results from the literature, and determine several spin correlation functions. Our `best estimates' for the ground state correlation functions do not depend sensitively on the input trial wave function of the fixed-node projection, and are reasonably close to the exact values. We also calculate the spin gap of the model with the Fixed-Node Monte Carlo method. For this it is necessary to use a many-Slater-determinant trial state. The lowest-energy spin excitation is a running spin soliton with wave number pi, in agreement with earlier calculations.
19 pages, revtex, contribution to Festschrift for Hans van Leeuwen