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Let's say I want to calculate the energy spectrum of Heisenberg model:
$ H = J \sum \limits_{\langle i,j \rangle} \vec S_i \cdot \vec S_j -g ~\mu_B \sum \limits_{i} \vec S_i \cdot \vec B$
but value of $J$ is given as $J/k_B= 20 ~K $ (kelvin). now If I put $J= 20 * 1.38* 10^{−23} $ joule in $H$ an...
