namespace rgpot_sw

Overview

Stillinger-Weber potential in gather form. More…

namespace rgpot_sw {
 
// global variables
 
real(wp), parameter exp_floor = -300.0_wp;
 
// global functions
 
subroutine, public sw_energy_forces(real(wp), dimension(:, :), intent(in), contiguous positions, real(wp), dimension(3, 3), intent(in) cell, type(sw_params_t), intent(in) par, type(neighbor_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

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

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

subroutine, public sw_energy_forces(real(wp), dimension(:, :), intent(in), contiguous positions, real(wp), dimension(3, 3), intent(in) cell, type(sw_params_t), intent(in) par, type(neighbor_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.