enable single-node optimization, add test_1f

Closes Issue #606 (if applicable).

Changes proposed in this Pull Request

Allow for single-node optimization, add test_1f

[x] Code changes have been tested locally.
[ ] Code changes are sufficiently documented, i.e. new functions contain docstrings and further explanations may be given in docs.
[ ] A note for the release notes docs/files/release_notes.rst is included.
[ ] Breaking changes are documented in the docs and are communicated to the user (if applicable).
[ ] Newly introduced dependencies are added to pyproject.toml (if applicable).
[x] Tests for new features were added (if applicable).