How to use struqture objects

Struqture objects may be instantiated directly by the user or imported from a file or database. This section of the documentation explains both approaches and directs you to the remainder of the user guide once you are comfortable with them.

Creating your own Hamiltonians and operators

To create your own Hamiltonian or operator, simply import the corresponding python class from the spins module. For instance, to import an object corresponding to a Hamiltonian composed of spins, which can be represented by Pauli matrices, run:

from struqture_py.spins import PauliHamiltonian

In the spins section of the documentation we will explore the various classes in the spins module.

Using a struqture Hamiltonian from a file

Struqture objects can be stored as either JSON files or as binary code. We highly recommend using JSON files, as they are also human-readable. Struqture was designed not only to easily instantiate or modify objects, but also to easily exchange them with other users - this is where the JSON serialisation comes into play.

For instance, given a file storing our Hamiltonian, hamiltonian.json, we can import it in the following way:

from struqture_py.spins import PauliHamiltonian

# Reading a file: from_json
with open("hamiltonian.json", "r") as f:
    hamiltonian = PauliHamiltonian.from_json(f.read())

print(hamiltonian)

# Writing to a file: to_json
# Should you wish to perform the inverse operation (writing your Hamiltonian to a file), you can
# do so by running the following lines of code:
with open("hamiltonian.json", "w") as f:
    f.write(hamiltonian.to_json())

Once a struqture object (e.g. a Hamiltonian or operator) has been loaded from a file, it can be used in the same manner as one created by the user. Refer to the remaining documentation for the available getters, setters, and properties.

Using a struqture Hamiltonian from a database

In this part of the user documentation we show how to work with a user-selected pre-defined Hamiltonian from our database, e.g. nmr_database.

For instance, this code snippet shows how to load the C6H5NO2 molecule from the hqs_nmr_parameters database, and turn it into a struqture object:

from hqs_nmr_parameters import examples, nmr_hamiltonian

parameters = examples.molecules["C6H5NO2"]
hamiltonian = nmr_hamiltonian(parameters=parameters, field=2.5)

Once a struqture object (e.g. a Hamiltonian or operator) has been loaded from a databse, it can be used in the same manner as one created by the user. Refer to the remaining documentation for the available getters, setters, and properties.