quemb.molbe.solver.solve_ccsd

quemb.molbe.solver.solve_ccsd(mf, frozen=None, mo_coeff=None, relax=False, use_cumulant=True, with_dm1=True, rdm2_return=False, mo_occ=None, mo_energy=None, rdm_return=False, verbose=0)

Solve the CCSD (Coupled Cluster with Single and Double excitations) equations.

This function sets up and solves the CCSD equations using the provided mean-field object. It can return the CCSD amplitudes (t1, t2), the one- and two-particle density matrices, and the CCSD object.

Parameters:

  • mf (RHF) – Mean-field object from PySCF.

  • frozen (list or int, optional) – List of frozen orbitals or number of frozen core orbitals. Defaults to None.

  • mo_coeff (ndarray, optional) – Molecular orbital coefficients. Defaults to None.

  • relax (bool, optional) – Whether to use relaxed density matrices. Defaults to False.

  • use_cumulant (bool, optional) – Whether to use cumulant-based energy expression. Defaults to True.

  • with_dm1 (bool, optional) – Whether to include one-particle density matrix in the two-particle density matrix calculation. Defaults to True.

  • rdm2_return (bool, optional) – Whether to return the two-particle density matrix. Defaults to False.

  • mo_occ (ndarray, optional) – Molecular orbital occupations. Defaults to None.

  • mo_energy (ndarray, optional) – Molecular orbital energies. Defaults to None.

  • rdm_return (bool, optional) – Whether to return the one-particle density matrix. Defaults to False.

  • verbose (int, optional) – Verbosity level. Defaults to 0.

Returns:

  • t1 (numpy.ndarray): Single excitation amplitudes.

  • t2 (numpy.ndarray): Double excitation amplitudes.

  • rdm1a (numpy.ndarray, optional): One-particle density matrix

    (if rdm_return is True).

  • rdm2s (numpy.ndarray, optional): Two-particle density matrix

    (if rdm2_return is True and rdm_return is True).

  • mycc (pyscf.cc.ccsd.CCSD, optional): CCSD object

    (if rdm_return is True and rdm2_return is False).

Return type:

tuple