— notes that the application can be recompiled to provide support for XYZ two-spin interactions but I haven't yet figured out how that can be done (nor how it would be re-integrated into the full ALPS package).
Best Regards,
Nat Fortune
background: A colleague of mine used the ALPS/looper package to carry out QMC calculations of the magnetic-field-dependent phase boundary for a S = 1/2 Heisenberg system with weak easy-plane (XY) anisotropy. He did this by setting the spin-Hamiltonian parameters Jz/Jxy = 0.995. This corresponds to $\frac{\Delta}{J} = 0.005$, where the Hamiltonian is given by the following equation:
\begin{equation}
H = J \sum_{nn}[S_{i}^{x} S_{j}^{x}+ S_{i}^{y} S_{j}^{y} + ( 1 -\Delta ) S_{i}^{z} S_{j}^{z}] + J_{\perp}\sum_{i,i'} \boldsymbol{S}_{i} \cdot \boldsymbol{S}_{i'}-g \mu_B \boldsymbol{H}\cdot \sum_{j}\boldsymbol{S}_j
\label{eq:Xiao2009Hamiltonian}
\end{equation}
and the first summation is over nearest neighbors, the second summation links each spin to its
counterparts in adjacent layers, and the third summation includes all spins.
Unfortunately for us, experiments now reveal that the experimental system we want to model is better described by a biaxial asymmetry within the XY plane, where $\Delta = 0.003$ would be replaced by $\Delta_{z} = 0.003$ and $\Delta_{y} = 0.0003$, where the Hamiltonian is given by the following equation:
\begin{equation}
H = J \sum_{i,j}[S_{i}^{x} S_{j}^{x}+ ( 1 -\Delta_y ) S_{i}^{y} S_{j}^{y} + ( 1 -\Delta_z ) S_{i}^{z} S_{j}^{z}] -g \mu_B \boldsymbol{H}\cdot \sum_{j}\boldsymbol{S}_j + J_{\perp}\sum_{i,i'} \boldsymbol{S}_{i} \cdot \boldsymbol{S}_{i'} \label{eq:NewHamiltonian}
\end{equation}
--
Professor Nathanael Fortune, Ph.D.
Department of Physics
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44 College Lane
Smith College
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"The great tragedy of Science — the slaying of a beautiful hypothesis by an ugly fact." T.H. Huxley