Ferromagnetic state of spin-1 chain

ITensor Julia Questions
1

Hi,

I would like to investigate the time evolution of the ferromagnetic state of a spin-1 chain as an initial state ‘|Psi0>’ in which all spins are down(up). In the Hamiltonian, I would consider external magnetic fields in the x and z directions applying just on the first spin. How can I reproduce the ferromagnetic state ‘|Psi0>’ as initial state?

2

To prepare a product state, you can use the MPS function like this:

s = siteinds("S=1",N)
psi0 = MPS(s,"Dn")

If you want all the spins to be up instead, you can use psi0 = MPS(s,"Up"). To make a non-uniform pattern, you can pass an array of the strings “Up”, “Dn”, or “Z0” (for “S=1” type sites).

Here are some relevant parts of the documentation:

  1. information on available state names (like “Up”, “Z0”, “Dn”) for different site types:
    https://itensor.github.io/ITensors.jl/dev/IncludedSiteTypes.html
  2. documentation on MPS constructors:
    https://itensor.github.io/ITensors.jl/dev/MPSandMPO.html#ITensors.MPS-Tuple{Vector{<:Index},%20Any}