First H₂ calculation

Run neutral singlet H₂ with STO-3G from the repository root:

cargo run --locked -- basis import tests/data/sto-3g.json
cargo run --locked -- run samples/h2/sto-3g/calculation.toml

Import writes the checked-in basis fixture to the application’s local basis store, avoiding a network download. CLI tests import the same fixture into an isolated store.

The checked-in configuration is included directly:

[basis]
name = "sto-3g"

[molecule]
geometry = "../molecule.xyz"

[method.hf.guess]
type = "CoreHamiltonian"

The geometry path resolves from the runfile directory. Preserve the directory layout if copying the sample. Its XYZ source is:

2
Hydrogen molecule
1 0.0 0.0 -0.37
H 0.0 0.0  0.37

Default input units are Angstrom; resolved coordinates are Bohr. The neutral singlet defaults resolve HF Auto to RHF. The core-Hamiltonian guess makes this example deterministic.

The existing CLI regression test checks this input, RHF resolution, units, two SCF iterations, and these selected output lines. Its reproducible command is below; the test source is linked for readers who want to inspect its assertions.

CLI test source on GitHub

SCF converged after 2 iterations.
Total Energy (including nuclear repulsion): -1.116759 Hartree

Run that verification with:

cargo test --locked --test cli_samples test_cli_h2_sample_converges_and_prints_reference_energy

For independent numerical verification, the h2-sto-3g-rhf case compares full precision JSON energies against PySCF with a 2e-10 Hartree energy tolerance. The rounded terminal value above is not that tolerance. See the book’s scientific scope and reference comparisons for the coverage boundary. The comparison implementation and full reference instructions are linked below.

Comparison source on GitHub

Reference test instructions on GitHub

nix run .#pyscf-check -- -k h2-sto-3g-rhf

These checks validate this case, not arbitrary chemistry. Results remain experimental and require independent validation before research use. Continue with output interpretation. To save and reuse the calculation’s AO ERIs, continue with the portable bundle guide.