Quick Start: Ground State Search

In this quick start, we show the basic usage of the TTNOpt package for the ground state search of the quantum spin systems.

Creating Input Files

First, specify the model and parameters of the Hamiltonian and set up the computational method. Each file should be written according to the paper.

Samples of the input files are provided in the sample directory. Input files are written in YAML format and looks like the following:

input.yml

system:
   N: 8 # Number of spins
   spin_size: 1/2

   # Exchange coupling for the XXZ or XYZ model
   model:
      type: XYZ # Choose XXZ or XYZ
      file: XYZ.dat # Pair-variable file containing J_{i,j}, Δ_{i,j}  or Jx_{i,j}, Jy_{i,j}, Jz_{i,j}

numerics:
   init_tree: 0 # If 0, the initial structure is MPN
   opt_structure:
      type: 1 # 0: no optimization, 1: structural optimization
   initial_bond_dimension: 20
   max_bond_dimensions: [20, 40, 60, 80] # Maximum bond dimension for each repetition
   max_num_sweeps: [20, 10, 7, 5]
   energy_convergence_threshold: 1e-11
   entanglement_convergence_threshold: 1e-10
   energy_degeneracy_threshold: 1e-13
   entanglement_degeneracy_threshold: 0.1

output:
   dir: data
   single_site: 0
   two_site: 0

Execution

Use the name of the input file created above as an argument and execute the TTNOpt ground state search with the following command:

gss input_file_name

Execution Results

The execution results are output to the specified folder.