Grid

The Grid in Octopus

Introduction

The fundamental element of Octopus is the real space grid, on which all quantities, such as wave functions, densities and potentials are defined.

In general, a grid consists of

• the mesh
• the simulation box

The mesh is based on an regular mesh in D dimensions, which can be distorted using so-called curvilinear coordinates.

The underlying internal structure is a mesh of integer coordinates and the important mapping arrays which

• map the index to the D integer coordinates
• map the integer coordinates to the index.

The grid is constructed in several steps:

1. Generation of a regular mesh filling a rectangular volume enclosing the simulation box.
2. Selecting inner points, enlargement points and ghost points.
3. re-ordering the points and regeneration of the mapping arrays.

The top level data structure, describing a grid is defined in grid/grid.F90:

  type, extends(mesh_t) :: grid_t
    ! Components are public by default
    type(derivatives_t)         :: der
    type(stencil_t)             :: stencil
    type(symmetries_t)          :: symm
    type(symmetrizer_t)         :: symmetrizer
  end type grid_t

• Simulation Box
• Mesh implementation
• Mesh Setup
• Mesh operations
• Derivatives
• Coordinate systems