---
title: Operator Library (latest version)
description: API reference for Operator Library in the latest version of qiskit-fermions-c
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-fermions-c/qf-operators-library
---

# Operator Library

The C API provides various functions to simplify the construction of commonly used operators.

## Commutator Generators

|                                                                                                                                            |                                                    |
| ------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------- |
| [`qf_op_type_commutator()`](/docs/api/qiskit-fermions-c/qf-commutators#qf_op_type_commutator "qf_op_type_commutator")                      | Computes the commutator of two operators.          |
| [`qf_op_type_anti_commutator()`](/docs/api/qiskit-fermions-c/qf-commutators#qf_op_type_anti_commutator "qf_op_type_anti_commutator")       | Computes the anti-commutator of two operators.     |
| [`qf_op_type_double_commutator()`](/docs/api/qiskit-fermions-c/qf-commutators#qf_op_type_double_commutator "qf_op_type_double_commutator") | Computes the double-commutator of three operators. |

## Common Operators

This section provides a quick reference for various operator constructor functions, grouped by category.

### Electronic Integrals

|                                                                                                                                                                          |                                                                    |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------ |
| [`qf_ferm_op_from_1body_tril_spin_sym()`](/docs/api/qiskit-fermions-c/qf-electronic-integrals#qf_ferm_op_from_1body_tril_spin_sym "qf_ferm_op_from_1body_tril_spin_sym") | Constructs from spin-symmetric triangular 1-body integrals.        |
| [`qf_ferm_op_from_1body_tril_spin()`](/docs/api/qiskit-fermions-c/qf-electronic-integrals#qf_ferm_op_from_1body_tril_spin "qf_ferm_op_from_1body_tril_spin")             | Constructs from separate spin-species triangular 1-body integrals. |
| [`qf_ferm_op_from_2body_tril_spin_sym()`](/docs/api/qiskit-fermions-c/qf-electronic-integrals#qf_ferm_op_from_2body_tril_spin_sym "qf_ferm_op_from_2body_tril_spin_sym") | Constructs from spin-symmetric triangular 2-body integrals.        |
| [`qf_ferm_op_from_2body_tril_spin()`](/docs/api/qiskit-fermions-c/qf-electronic-integrals#qf_ferm_op_from_2body_tril_spin "qf_ferm_op_from_2body_tril_spin")             | Constructs from separate spin-species triangular 2-body integrals. |

## Other Generators

Finally, the following additional operator generator utilities exist:

|                                                                             |                                                        |
| --------------------------------------------------------------------------- | ------------------------------------------------------ |
| [`QfFCIDump`](/docs/api/qiskit-fermions-c/qf-fcidump#qffcidump "QfFCIDump") | An electronic structure Hamiltonian in FCIDump format. |