Ground state of a triangular quantum antiferromagnet: Fixed-node Green-function Monte Carlo study

A recently proposed ''fixed-node'' quantum Monte Carlo scheme for lattice Hamiltonians is adopted to study antiferromagnetic order of the Neel type in the ground state of the two-dimensional spin-1/2 antiferromagnetic Heisenberg model on the triangular lattice. Fixed-node Green-function Monte Carlo simulations, based on an antiferromagnetically correlated trial wave function, are performed on lattices of up to 324 sites. Extrapolation of the results to the thermodynamic limit indicates that an ordered ground state may exist with a sublattice magnetization of as much as similar to 60% of the classical value; an upper bound of - 0.5431 +/- 0.0001 J is found for the ground-state energy per site.