Q5.4 (b)+(c), Bragg Williams Approximation

Posted by A on April 1, 2014, 10:23 pm

Hi, I got stuck on the derivation of the approximate expectation of the Hamiltonian in part (b) and (c) of question 5.4: using =-J(NP''+NP,,-NP',)+gmuB(NP'-NP,) where P'' is the probability for two neighbouring sites to have spin up, P'' spin down etc, I find that =-2JNZs^2+2gmuBNs, so s being out by a factor of 2... This text on page 67 http://www.scribd.com/doc/52012078/27/Bragg%E2%80%94Williams-Approximation uses s=m/2 and arrives at the desired form with m rather than s, but then in the problem the logs are using s as defined above. What am I doing wrong here?

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Message Thread Q5.4 (b)+(c), Bragg Williams Approximation - A April 1, 2014, 10:23 pm Re: Q5.4 (b)+(c), Bragg Williams Approximation - Steve Simon April 1, 2014, 10:47 pm Re: Q5.4 (b)+(c), Bragg Williams Approximation - A April 1, 2014, 10:58 pm « Back to index

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