Variational Hilbert-space-truncation approach to quantum Heisenberg antiferromagnets on frustrated clusters

Abstract

We study the spin-1/2 Heisenberg antiferromagnet on a series of finite-size clusters with features inspired by the fullerenes. Frustration due to the presence of pentagonal rings makes such structures challenging in the context of quantum Monte Carlo methods. We use an exact diagonalization approach combined with a truncation method in which only the most important basis states of the Hilbert space are retained. We describe an efficient variational method for finding an optimal truncation of a given size which minimizes the error in the ground-state energy. Ground-state energies and spin-spin correlations are obtained for clusters with up to 32 sites without the need to restrict the symmetry of the structures. The results are compared to full-space calculations and to unfrustrated structures based on the honeycomb lattice.