Density matrix renormalisation group for a quantum spin chain at non-zero temperature

TL;DR

This paper demonstrates that a modified DMRG method can effectively compute thermodynamic properties of a quantum spin chain at non-zero temperatures, especially when an energy gap is present, using a small basis set.

Contribution

The study applies a recent adaptation of DMRG to a quantum spin model at finite temperature, showing its effectiveness and accuracy in low-temperature regimes.

Findings

Accurate thermodynamic functions at low temperatures with small basis sets.

Best accuracy achieved when the system has a substantial energy gap.

DMRG is applicable to quantum systems at non-zero temperature.

Abstract

We apply a recent adaptation of White's density matrix renormalisation group (DMRG) method to a simple quantum spin model, the dimerised $XY$ chain, in order to assess the applicabilty of the DMRG to quantum systems at non-zero temperature. We find that very reasonable results can be obtained for the thermodynamic functions down to low temperatures using a very small basis set. Low temperature results are found to be most accurate in the case when there is a substantial energy gap.