ffsim.sample_slater

ffsim.sample_slater(norb, occupied_orbitals, orbital_rotation=None, *, orbs=None, shots=1, concatenate=True, bitstring_type=BitstringType.STRING, seed=None)[source]

Collect samples of electronic configurations from a Slater determinant.

The Slater determinant is specified as an orbital rotation applied to the reference electronic configuration given by occupied_orbitals. The sampler draws independent samples from the corresponding determinantal point process using the projection-based sequential sampling algorithm described in the reference below.

References

Parameters:

  • norb (int) – The number of spatial orbitals.

  • occupied_orbitals (Sequence[int] | tuple[Sequence[int], Sequence[int]]) – The occupied orbitals in the electronic configuration. This is either a list of integers specifying spinless orbitals, or a pair of lists, where the first list specifies the spin alpha orbitals and the second list specifies the spin beta orbitals.

  • orbital_rotation (ndarray | tuple[ndarray | None, ndarray | None] | None) – The optional orbital rotation. Either a single Numpy array specifying the orbital rotation to apply to both spin sectors, or a pair of Numpy arrays specifying independent orbital rotations for spin alpha and spin beta. In the paired form, None indicates that the identity operation is applied to the corresponding spin sector.

  • orbs (Sequence[int] | tuple[Sequence[int], Sequence[int]] | None) – The orbitals to sample. In the spinless case, this is a list of integers in range(norb). In the spinful case, this is a pair of such lists, where the first list stores spin-alpha orbitals and the second list stores spin-beta orbitals. If not specified, then all orbitals are sampled.

  • shots (int) – The number of bitstrings to sample.

  • concatenate (bool) – Whether to concatenate the spin-alpha and spin-beta parts of the bitstrings. If True, then a single list of concatenated bitstrings is returned. The strings are concatenated in the order \(s_b s_a\), that is, the alpha string appears on the right. If False, then two lists are returned, (strings_a, strings_b), with the alpha strings listed first. In the spinless case (when occupied_orbitals is a sequence of integers), this argument is ignored.

  • bitstring_type (BitstringType) – The desired type of bitstring output.

  • seed (Generator | int | None) – A seed to initialize the pseudorandom number generator. Should be a valid input to np.random.default_rng.

Return type:

Sequence[int] | Sequence[str] | ndarray

Returns:

The sampled bitstrings.