Atomic Structure Explorer

Atomic Structure Explorer is an interactive desktop application for undergraduate atomic physics. It shows how a central-field calculation leads from radial orbitals to electron configurations, spectroscopic terms, and approximate fine-structure levels.

Calculations run locally, so the application works offline after installation.

Download

Open the repository’s Releases page and download the installer for your computer:

• Windows x64: AtomicStructureExplorer-Windows-x64-Setup.exe
• Apple Silicon Mac: AtomicStructureExplorer-macOS-arm64.dmg

On Windows, run the setup program and choose whether to create a desktop shortcut. On macOS, open the disk image and drag Atomic Structure Explorer to the Applications shortcut.

The current downloads are unsigned development builds. Windows SmartScreen or macOS Gatekeeper may display a warning. If you would rather not run an unsigned application, follow the source-installation instructions below.

Quick start

1. Choose an element

The opening screen is an interactive periodic table. Select an element to calculate its neutral-atom orbitals and ground configuration.

Blue tiles identify the implemented one-valence teaching family and green tiles the two-valence family. Every element supports the central-field and configuration views; the more detailed features depend on the element’s valence structure.

2. Follow the four stages

Use the numbered buttons across the top of the workspace:

1. Central field shows the calculated one-electron orbitals.
2. Configuration shows how those orbitals are occupied and compares the calculated filling with the accepted ground-state configuration.
3. Terms shows the supported spectroscopic terms produced by residual electrostatic interactions.
4. Fine structure resolves supported terms into approximate spin-orbit levels.

The energy diagram changes as you move between stages. If the selected atom is outside the implemented term or fine-structure models, the application explains that boundary instead of inventing a result.

3. Explore the radial orbitals

The Radial orbitals panel plots radial probability against radius on a logarithmic scale.

• Each orbital has a colour-matched legend entry.
• Move the pointer over a curve to see its orbital label, energy, and occupation.
• Compare the positions and penetration of s, p, d, and f orbitals.

4. Examine quantum defects for alkali metals

For alkali-metal atoms, open the Quantum defects tab below the energy diagram. It lists calculated Rydberg-series binding energies and quantum defects for different angular momenta.

Try sodium to see the characteristic ordering δs > δp > δd ≈ 0. For other element families, the tab explains why this particular analysis is unavailable.

5. Read the explanation and calculation log

The tabs on the right provide different levels of detail:

• Learn explains the physical step represented by the selected stage.
• Calculation log exposes the numerical and modelling decisions made during the calculation.
• Compare places the calculated electron filling beside the accepted configuration and states the reference-data limitations.

The status and warning areas identify convergence results, LS-coupling limits, and other cautions that affect interpretation.

Things to try

• Hydrogen: compare the familiar Coulomb orbitals and level structure.
• Sodium: inspect Rydberg levels, quantum defects, and spin-orbit doublets.
• Magnesium: compare singlet and triplet terms for a two-valence-electron example.
• Chromium or copper: inspect how competing occupations produce their well-known filling exceptions.
• A heavier atom: explore its central-field orbitals and note where the detailed model stops.

Interpreting the results

Atomic Structure Explorer is a teaching model rather than a precision spectroscopy package.

• Hydrogen uses the exact Coulomb central field.
• Multi-electron atoms use a numerical spherical Hartree self-consistent field with local Dirac/Slater exchange and a Latter tail correction.
• The local exchange approximation is not exact Hartree–Fock.
• Correlation and relativistic effects are not treated systematically.
• Detailed term and fine-structure calculations are limited to selected valence structures.
• Calculated orbital and level energies should not be treated as precision experimental transition data.

Run from source

Python 3.11 or newer is required.

python -m venv .venv
python -m pip install -e ".[dev]"
python -m atomic_structure_explorer

Activate the virtual environment before installing when required by your shell. On Windows PowerShell:

.venv\Scripts\Activate.ps1

Run the tests with:

python -m pytest

Licence

Released under the MIT License.