The ALPS Project provides an state-of-the-art library for numerical simulations on strongly correlated quantum systems. Here, I present an extension for the library and the exact diagonalization routines (fulldiag and sparsediag) which allows us to obtain different quantum correlation measures for the simulated model. Also, it allow us to recover the density matrix of any subsystem.
Results are stored both on xml and hdf5
Here you can download a pre-alpha release of the extension.
Quick resume
To define a subsystem called A, corresponding to the first two sites in the lattice, we add the line
SUBSYSTEM[A] ="sites(0,1)"
In order to recover the density matrix of the state associated to the subsystem A,
ENTANGLEMENT_MEASURE[Local state A]="state(A)"
For the diag routines, it generates at the end of the calculus a folder
"/localsystems" on the output hdf5 file.
On the subfolder "definitions" we can access to the list of sites which constitutes each each subsystem defined.
On the subfolder "states" we can access to each density matrices stored. They are stored as a list of pairs (weight,state). The density matrix can be recovered as
Sum(weight[i] state state^{\dagger},i) + (1-sum(weight[i],i)) Id/(dimension)