oqp.library.oqp_irc
===================

.. py:module:: oqp.library.oqp_irc

.. autoapi-nested-parse::

   .. code-block:: text

      OQP intrinsic reaction coordinate (IRC) for OpenQP.

      Backend-agnostic (NumPy only) Gonzalez--Schlegel mass-weighted steepest-descent
      reaction path (Gonzalez & Schlegel, J. Phys. Chem. 94, 5523 (1990)).

      The IRC is the steepest-descent path in mass-weighted Cartesian coordinates
      q = M^{1/2} x.  Each step of mass-weighted arc length ``s`` is taken with the
      Gonzalez--Schlegel constrained scheme:

        1. pivot point  q* = q_k - (s/2) g_hat   (g_hat = mass-weighted gradient dir);
        2. find q_{k+1} on the hypersphere |q - q*| = s/2 that minimizes E, i.e. the
           point whose gradient is radial (no tangential component).

      The first point is displaced from the transition state along the
      imaginary-frequency mode (mass-weighted), in the requested forward/backward
      direction.  The caller supplies ``energy_gradient(x_flat) -> (E, g_flat)`` in
      atomic units, so this module is testable on analytic surfaces without the OQP
      core.



Classes
-------

.. autoapisummary::

   oqp.library.oqp_irc.IRC


Functions
---------

.. autoapisummary::

   oqp.library.oqp_irc.imaginary_mode


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

.. py:class:: IRC(mass, x_ts, init_direction_mw, step=0.1, sign=1, logger=None)

   .. py:attribute:: sqm


   .. py:attribute:: x_ts


   .. py:attribute:: dir


   .. py:attribute:: step


   .. py:attribute:: sign
      :value: 1



   .. py:attribute:: logger
      :value: None



   .. py:method:: run(energy_gradient, max_points=50, gtol=0.0001, micro_max=6, micro_tol=0.0001, on_point=None)


.. py:function:: imaginary_mode(mass, hessian, coordinates=None, negative_tol=1e-08)

   .. code-block:: text

      Return the unique imaginary mode of a first-order saddle Hessian.

      ``mass`` in amu (natom,), ``hessian`` in Hartree/Bohr**2 (3N,3N), and
      optional ``coordinates`` in Bohr.  With coordinates, translations and
      rotations are projected before diagonalization so their near-zero
      numerical curvature cannot be mistaken for imaginary vibrations. Returns
      the normalized mass-weighted eigenvector and curvature. Numerical negative
      noise above ``-negative_tol`` is ignored. A valid IRC start must contain
      exactly one significant vibrational negative mode; minima and higher-order
      saddles are rejected.