:orphan:
 

.. index:: *MOLGRD
.. _*MOLGRD:

========
\*MOLGRD
========

The section gives directives for control of a single point evaluation of
the molecular gradient activated with :ref:`PROPERTIES_.MOLGRD` under :ref:`**PROPERTIES`.

The molecular gradient module is usually called from within the geometry
optimization module.


**Advanced options**

.. index:: .TRICK
.. _MOLGRD_.TRICK:

.TRICK
------

If activated the calculation of the SL and SS two-electron integral
contributions to the gradient is skipped if their contribution is
estimated to be small. An "empirical" estimate of the norms of the LS
and SS two-electron gradients based on the norm of the LL two-electron
gradient. If deactivated all contributions to gradient are calculated
and if activated then only "necessary" contributions are calculated.

*Default:* Deactivated.

.. index:: .INTFLG
.. _MOLGRD_.INTFLG:

.INTFLG
-------

Specify what two-electron integrals to include
(default: :ref:`HAMILTONIAN_.INTFLG` under :ref:`**HAMILTONIAN`).

.. index:: .SCREEN
.. _MOLGRD_.SCREEN:

.SCREEN
-------

Screening threshold.

*Default:*

::

    .SCREEN
     1.0D-17

Which means that screening is turned off by default. This is due to an
enormous demand of memory.

**Programmers options**

.. index:: .PRINT
.. _MOLGRD_.PRINT:

.PRINT
------

Print level.

A print level of less than 3 gives only the total gradient. Print levels
from 3+ gives individual contributions to the gradient (kinetic energy
gradient, nuclear attraction gradient etc.). Print levels of 5+ print
some matrices, and 10+ give massive output!

*Default:* Print level :ref:`GENERAL_.PRINT` from :ref:`**GENERAL`.

.. index:: .NUMGRA
.. _MOLGRD_.NUMGRA:

.NUMGRA
-------

Calculate the molecular gradient using numerical differentiation.

*Default:* Analytical evaluation if implemented.