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Experiments demand efficient methods to compute
thermodynamic properties of quantum magnets in
arbitrary dimensions and with arbitrary
interaction geometries as well as spin quantum
numbers S at moderate to high temperatures.
Using the square lattice as a reference system,
we start by generating reference data for
S<5/2 by Quantum Monte Carlo simulations and
for S=∞ by classical Monte Carlo
simulations. Next, we perform a phenomenological
scaling analysis with spin quantum number S.
We then explore other, mainly semiclassical
methods, which avoid expensive numerical
simulations. The methods investigated include
linearized spin-wave theory, equations of motion
for the Green functions, and a Monte-Carlo
evaluation of a cumulant expansion in a
spin-coherent-states representation.
A comparison of the advantages and shortcomings
of the different methods will be presented.
This work is performed in collaboration with M.E. Zhitomirsky from the CEA Grenoble and Johannes Richter from Magdeburg University. |
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