forte2.scf.scf_utils
====================

.. py:module:: forte2.scf.scf_utils




Module Contents
---------------

.. py:function:: minao_initial_guess(system, H)

   
   Generate a superposition of atomic potentials (SAP) initial guess for the SCF procedure
   S. Lehtola, J. Chem. Theory Comput. 15, 1593-1604 (2019), arXiv:1810.11659.
   For details, see https://doi.org/10.1063/5.0004046


   :Parameters:

       **system** : forte2.System
           The system object containing the atoms and basis set.

       **H** : NDArray
           The Fock matrix.

       **S** : NDArray
           The overlap matrix.



   :Returns:

       NDArray
           The initial MO guess for the SCF procedure.











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.. py:function:: core_initial_guess(system: forte2.system.System, H)

   
   Generate an initial guess by diagonalizing the core Hamiltonian.


   :Parameters:

       **system** : forte2.System
           The system object containing the atoms and basis set.

       **H** : NDArray
           The core Hamiltonian matrix.



   :Returns:

       NDArray
           The initial MO guess for the SCF procedure.











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.. py:function:: guess_mix(C, homo_idx, mixing_parameter=np.pi / 4)

   
   Induce the breaking of S^2 symmetry for UHF ms=0.0 calculations.
   This is helpful for obtaining proxies for open-shell singlets, for example.


   :Parameters:

       **C** : NDArray
           The MO coefficients.

       **homo_idx** : int
           The index of the highest occupied molecular orbital (HOMO).

       **mixing_parameter** : float, optional
           The mixing parameter for the Givens rotation.

       **twocomp** : bool, optional
           Whether the system is two-component.



   :Returns:

       NDArray
           The modified MO coefficients.








   .. rubric:: Notes

   See Szabo and Ostlund Ch. 3.8.7.



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.. py:function:: guess_mix_ghf(C, ha, hb, la, lb, mixing_parameter=np.pi / 4)

   
   Induce the breaking of S^2 symmetry for UHF ms=0.0 calculations.
   This is helpful for obtaining proxies for open-shell singlets, for example.


   :Parameters:

       **C** : NDArray
           The MO coefficients.

       **ha** : int
           The index of the highest occupied alpha(-like) orbital.

       **hb** : int
           The index of the highest occupied beta(-like) orbital.

       **la** : int
           The index of the lowest unoccupied alpha(-like) orbital.

       **lb** : int
           The index of the lowest unoccupied beta(-like) orbital.

       **mixing_parameter** : float, optional
           The mixing parameter for the Givens rotation.



   :Returns:

       NDArray
           The modified MO coefficients.








   .. rubric:: Notes

   See Szabo and Ostlund Ch. 3.8.7.



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.. py:function:: alpha_beta_mix(C, mixing_parameter=0.1)

   
   Induce the breaking of S_z symmetry for GHF calculations.
   This function explicitly mixes the degenerate alpha and beta MOs,
   which results in non-vanishing D_ab/D_ba density matrix elements.


   :Parameters:

       **C** : NDArray
           The MO coefficients.

       **mixing_parameter** : float, optional
           The mixing parameter for the Givens rotation.



   :Returns:

       NDArray
           The modified MO coefficients.











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.. py:function:: break_complex_conjugation_symmetry(C, pert_strength=0.1)

   
   Break the time-reversal/complex conjugation symmetry of the MO coefficients.
   A random phase is applied to each AO (cannot be MO as it would not change the density matrix).


   :Parameters:

       **C** : NDArray
           The MO coefficients.

       **pert_strength** : float, optional
           The strength of the perturbation (in radians).



   :Returns:

       NDArray
           The modified MO coefficients.











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