New subject: uniform susceptibility

23 Jan 2009

      On Fri, 23 Jan 2009 12:00:04 +0100, comp-phys-alps-users-request wrote
...

uniform susceptibility (Tadeusz Wasiutynski)

Message: 2
Date: Thu, 22 Jan 2009 12:55:44 +0100
From: "Tadeusz Wasiutynski" Tadeusz.Wasiutynski@ifj.edu.pl
Subject: [ALPS-users] uniform susceptibility
To: comp-phys-alps-users@phys.ethz.ch
Message-ID: 20090122115137.M49749@ifj.edu.pl
Content-Type: text/plain;	charset=iso-8859-2
hello,
I try to understand all examples in alps-applications. How can I 
figure out what exactly is in the output as "uniform susceptibility" 
(say in Ising) and why it is not simply <M2>-<M>2? In which part of 
the code it is hidden? Tadeusz

Message: 4
Date: Thu, 22 Jan 2009 23:10:11 +0900 (JST)
From: Synge Todo wistaria@comp-phys.org
Subject: Re: [ALPS-users] uniform susceptibility
To: comp-phys-alps-users@phys.ethz.ch, Tadeusz.Wasiutynski@ifj.edu.pl
Message-ID: 20090122.231011.245963879.wistaria@comp-phys.org
Content-Type: Text/Plain; charset=us-ascii
If 'M' means the total uniform magnetization (i.e. M = \sum s_i^z),
the uniform susceptibility and <M2>-<M>2 differ by the factor \beta/N
(\beta = 1/T and N the number of sites).  If 'M' is the magnetization
per site (\sum s_i^z / N), then the factor becomes \beta \times N.
Synge
Thank you for prompt answer. There is still something unclear for me. When
running spinmc Ising model with say L=8 and T=1, square lattice, update
cluster, sweeps 100000 I get:
Magnetization^2 0.99862084
|Magnetization| 0.999285325
Susceptibility 63.911734
So it looks like Susceptibility=N * Magnetization^2
On the other hand given susceptibility at Tc scales very well with size.
Where do I make mistake?
Tadeusz