qat.fermion.chemistry.pyscf_tools.perform_pyscf_computation

qat.fermion.chemistry.pyscf_tools.perform_pyscf_computation(geometry: list, basis: str, spin: int, charge: int, run_fci: bool = False)

Perform various calculations using PySCF. This function is a helper function meant to kickstart molecule studies. Its use is completely optional, and using other methods or packages is entirely possible.

This function will compute:

• The reduced density matrix,

• The orbital energies,

• The nuclear repulsion constant,

• The number of electrons,

• The one- and two-body integrals,

• The groundstate energies obtained through Hartree-Fock and 2nd order Möller-Plesset perturbation approach,

• (Optional) The groundstate energy using the full configuration interaction (full CI) approach.

Note

• The FCI computation is very expensive for big molecules. Enable it only for small molecules !

Parameters

• geometry (list) –

  Defines the molecular structure. The internal format is PySCF format:

  atom = [[atom1, (x, y, z)],
          [atom2, (x, y, z)],
          ...
          [atomN, (x, y, z)]]
  

• basis (str) – Defines the basis set.

• spin (int) – 2S, number of alpha electrons - number beta electrons to control multiplicity. If spin is None, multiplicity

• molecule. (will be guessed based on the neutral) –

• charge (int) – Charge of molecule. Affects the electron numbers.

• run_fci (bool, optional) – Whether the groundstates energies should also be computed using a full CI approach. Defaults to False.

Returns

• rdm1 (np.ndarray): Reduced density matrix.

• orbital_energies (list): List of orbital energies.

• nuclear_repulsion (float): Nuclear repulsion constant.

• nels (int): Number of electrons.

• one_body_integrals (np.ndarray): One-body integral.

• two_body_integrals (np.ndarray): Two-body integral.

• info (dict): Dictionary containing the Hartree-Fock and 2nd order Möller-Plesset computed ground state energies (and optionally the Full CI energy if run_fci is set to True).

Return type

Tuple[np.ndarray, list, float, int, np.ndarray, np.ndarray, dict]