libGridXC API

Access to the library's functionality is provided by importing the gridXC module:

use gridxc

which exports the interfaces to the public user-level routines and other symbols.

Exported types and parameters

The library exports the kind parameter grid_p appropriate for the arrays passed to a from the cellXC routine. This is controlled by the setting of the --enable-single-precision configure option (by default, a double-precision kind is returned).

Initialization routine

It is necessary to call the gridxc_init routine before any other operations. Currently, this routine just sets a few internal variables. If working in parallel, the MPI communicator is passed in this call.

Selection of XC functionals

• The routine setXC and its simpler variants setXC_libxc_ids and setXC_family_authors select the functionals to use. The available functionals and the syntax for their specification are discussed in the Guide to functionals. This information is currently stored in global module variables, and can be retrieved with the getXC routine.

Main routines

Atomic (spherical) grids

• Routine atomXC computes the exchange-correlation energies and potential for a spherical charge density, as given in a radial grid.

Box (periodical) grids

• Routine cellXC is the major workhorse of the library. It computes the exchange-correlation energies and potential for a periodical charge density, represented in a (possibly distributed in parallel) parallepipedic grid.

Other exported functionality

(See the source for full documentation)

Convenience utilities

A few routines are exported for convenience to some user programs:

• nfft_gridxc: When VDW functionals are used, the library employs internally FFT routines that need the mesh sizes to be multiples of 2, 3, or 5. This routine (see the source) will help to determine the appropriate values.

• setmeshdistr/meshBox: These routines can be used to select an appropriate data distribution in parallel. See the source for more information. These are in the process of refactoring to make them truly stand-alone.

Lower level entry points

• gridxc_ldaxc
• gridxc_ggaxc