Integration of PSolver in SIESTA and Octopus¶
A Poisson solver is an efficient tool to determine electromagnetic fields produced by an electric charge distributed in space. The integration of PSolver into SIESTA and Octopus has opened the way for these software programs to access more complex physical systems. The PSolver library allows solving the Poisson equation in much more general ways than using Fourier Transforms.
Purpose of Module¶
The PSolver library solves the Poisson equation using wavelets. With this approximation one can more easily take into account certain boundary conditions such as molecules (no boundaries), wires (periodic along 1 direction) and slabs (periodic along 2 directions). This is in contrast to Fourier transforms which assumes periodic boundary conditions along all lattice vectors. Additionally it allows cavities for different dielectric constants.
This implementation integrates the PSolver library into the DFT codes SIESTA and Octopus such that they may be used for end-users who require the functionalities.
Background Information¶
Users of the SIESTA code have always been using the Fourier transforms for solving the Poisson equation. However, a great deal of users are dealing with, in particular, slab systems given the advent of graphene, 2D materials and surface calculations. This integration allows users to control the boundaries in a very strict way without any approximations. The latest PSolver library (shipped with BigDFT 1.9.0) will work.
Additional tests have been added to SIESTA to ensure that everything works.
The OCTOPUS code has various options to solve the Poisson equations. Amongst others were the ISF library, which is a predecessor of the PSolver library. In the later OCTOPUS versions, an older version of PSolver was packaged with the OCTOPUS sources. For the recently released OCTOPUS 10, the interface to PSolver has been updated, so that both the old and the new API of PSolver can be used. This also prepares OCTOPUS to use the GPU version of PSolver, once it becomes available. The configure scripts of OCTOPUS have been adapted to correctly detect and configure an installed PSolver library, and tests using the library have been added to the OCTOPUS buildbot.
Building and Testing¶
To compile SIESTA with PSolver users should add this to their arch.make
LIBS += -L<build-dir>/install/lib -lPSolver-1 -latlab-1 -lfutile-1 -ldicts -lfmalloc-1 -lyaml
INCFLAGS += -I<build-dir>/install/include
FPPFLAGS += -DSIESTA__PSOLVER
After building there are two tests, h2o_psolver and si2x1h-psolver which can be compared with h2o and
si2x1h, respectively. They should be comparable.
In order to compile OCTOPUS with the PSolver library, add the options --with-psolver-prefix and
--with-futile-prefix to the configure command of OCTOPUS:
./configure --with-psolver-prefix=<PSolver-top-dir> --with-futile-prefix=<Futile-top-dir> ...
The OCTOPUS test components/16-hartree_3d_psolver.test is testing the correct functionality of the PSolver
library in OCTOPUS.