We do single cluster Wolff-like updates. Hence if you are not close to the critical point the clusters are small and only few spins get updated. This makes for fast sweeps but longer autocorrelation times for the energy.

Matthias

On 22 Oct 2014, at 08:01, Rachele Nerattini <r.nerattini@gmail.com> wrote:

Dear ALPS community, 

I am writing for a question on the algorithm for classical Monte Carlo simulation of spin models. From the simulations I performed on classical O(2), O(3) and O(4) models it turned out that the autocorrelation time is quite large, let's say of about 80 o 90, for the energy density observable. I just would like to understand better if there is a particular reason for such a big tau and which kind of algorithm is really used for the simulation: 
Swendsen-Wang , Wolff single cluster or even something else? This is also because the term ”sweep” is quite unusual when cluster algorithms are concerned.

I really thank you all for your help. 

Best regards,

Rachele Nerattini

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   Rachele Nerattini
   Dip. di Fisica e Astronomia, Università di Firenze
   Via G. Sansone, 1, 50019 Sesto Fiorentino (FI), Italy
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