.. index:: pair: namespace; rgpot_sw
.. _doxid-namespacergpot__sw:

namespace rgpot_sw
==================

.. toctree::
	:hidden:

Overview
~~~~~~~~

Stillinger-Weber potential in gather form. :ref:`More...<details-namespacergpot__sw>`


.. ref-code-block:: cpp
	:class: doxyrest-overview-code-block

	
	namespace rgpot_sw {

	// global variables

	real(wp), parameter :ref:`exp_floor<doxid-namespacergpot__sw_1aae60c5415388517d2f7f73353efd2b51>` = -300.0_wp;

	// global functions

	subroutine, public :ref:`sw_energy_forces<doxid-namespacergpot__sw_1af6418e19490c418ad484332895331b53>`(real(wp), dimension(:, :), intent(in), contiguous positions, real(wp), dimension(3, 3), intent(in) cell, type(:ref:`sw_params_t<doxid-structrgpot__sw_1_1sw__params__t>`), intent(in) par, type(:ref:`neighbor_table_t<doxid-structrgpot__neighbors_1_1neighbor__table__t>`), intent(inout) table, real(wp), intent(out) energy, real(wp), dimension(:, :), intent(out), contiguous forces, integer, intent(out) status, character(len=:), intent(out), allocatable errmsg);

	} // namespace rgpot_sw
.. _details-namespacergpot__sw:

Detailed Documentation
~~~~~~~~~~~~~~~~~~~~~~

Stillinger-Weber potential in gather form.

The published SW expression sums a two-body term over pairs and a three-body term over triplets centred on each atom. Written as a scatter (one triplet updating three atoms) the atom loop carries dependencies; written as a gather each atom accumulates only its own force and the loop runs under ``do concurrent``.

An atom ``i`` collects three-body force in two roles:

* as the centre of a triplet ``(j, i, k)``, taking ``-(f_j + f_k)``;

* as an end of a triplet centred on a neighbour ``m``, taking the end-atom force of ``(i, m, k)`` for every other neighbour ``k`` of ``m``.

The two roles together reproduce the scatter sum exactly, at the cost of walking each neighbour's neighbour list. Energy accrues to the centre atom only, so it is counted once.

Global Variables
----------------

.. index:: pair: variable; exp_floor
.. _doxid-namespacergpot__sw_1aae60c5415388517d2f7f73353efd2b51:

.. ref-code-block:: cpp
	:class: doxyrest-title-code-block

	real(wp), parameter exp_floor = -300.0_wp

Exponential arguments below this underflow to zero; guarding keeps ``exp`` out of its denormal range for pairs at the cutoff.

Global Functions
----------------

.. index:: pair: function; sw_energy_forces
.. _doxid-namespacergpot__sw_1af6418e19490c418ad484332895331b53:

.. ref-code-block:: cpp
	:class: doxyrest-title-code-block

	subroutine, public sw_energy_forces(real(wp), dimension(:, :), intent(in), contiguous positions, real(wp), dimension(3, 3), intent(in) cell, type(:ref:`sw_params_t<doxid-structrgpot__sw_1_1sw__params__t>`), intent(in) par, type(:ref:`neighbor_table_t<doxid-structrgpot__neighbors_1_1neighbor__table__t>`), intent(inout) table, real(wp), intent(out) energy, real(wp), dimension(:, :), intent(out), contiguous forces, integer, intent(out) status, character(len=:), intent(out), allocatable errmsg)

Energy and forces for ``positions`` (3 x natoms) in ``cell``.