The Green X library is developed under Work Package 2 of the NOMAD Center of Excellence. It is available under the APACHE2 license.

• GX-AnalyticContinuation: Performs an analytical continuation of the self-energy from the imaginary frequency to the real frequency
• GX-LAPW: A cubic scaling GW algorithm in LAPW+lo basis.
• GX-LocalizedBasis: The implementation of the separable resolution of the identity.
• GX-PAW: Supports the projector-augmented wave method
• GX-PlaneWaves: Low-scaling plane-wave based GW implementation
• GX Time-frequency: Optimised quadrature grids and weights for RPA and GW imaginary time-frequency transforms.
• GX-q=0: A code-agnostic framework for the treatment of inverse dielectric function and/or screened Coulomb potential at q=0.

Green X has been designed as a collection of libraries, which can be built relatively independently of one another. To build the whole suite of Green X libraries from the source you need to have a Fortran compiler supporting Fortran 2008, and one of the supported build systems:

• cmake version 3.15.0 or newer, with a build-system backend, i.e. make.

Building with CMake

To build all libraries, set up a build directory, change to it and run cmake configuration:

mkdir build 
cd build
cmake ../

To explicitly specify the compiler, run CMake configure with:

FC=ifort cmake ../

Shared libraries are built by default. To build static versions, one can configure with:

cmake ../ -DBUILD_SHARED_LIBS=OFF

Specific shared libraries can be disable, e.g to disable the Projector-Augmented Wave (PAW) component of GreenX, run CMake configure with:

cmake ../ -DPAW_COMPONENT=OFF

Available options to disable one or more components

GreenX uses GNU Multiple Precision Arithmetic Library by default in the Analytical Continuation component, you can disable it without any harm by runing CMake configure with:

cmake ../ -DENABLE_GNU_GMP=OFF

GreenX uses submodules and they are built by default. You can obtained them by executing:

git submodule update --init --recursive

To build GreenX without the submodules, one can configure with:

cmake ../ -DCOMPILE_SUBMODULES=OFF

If all requirements are found, build and install the project:

make -j
make install 

Minimal example to build and install only the Time-Frequency component of GreenX:

cmake .. -DAC_COMPONENT=OFF -DLBASIS_COMPONENT=OFF -DPAW_COMPONENT=OFF -DCOMPILE_SUBMODULES=OFF
make -j
make install

GreenX uses pytest as its regression testing framework, in conjunction with the custom python module pygreenx. First, one must ensure that pygreenx is installed. From the GreenX root directory:

cd python
pip install -e .

One notes that the user may wish to change the scope of pip install to the Python user install directory of their platform. Typically ~/.local/. This can be achieved with:

pip install --user -e .

unless working in a virtual environment, in which case it is not required.

The test suite can now be run with CMake's ctest command:

cd build
ctest

GreenX is documented using Doxygen, and documentation support is disabled by default. To enable CMake looking for Doxygen, configure with:

cmake ../ -DENABLE_GREENX_DOCS=ON

To build the document, type in the build directory:

make docs

Documentation is built in documentation and can be viewed by opening html/index.html in a browser.

When adding new files with documentation, please ensure the directory is listed in the INPUT tag of Doxyfile.

For more information and benchmark examples see also the GreenX website.

Unit tests require the unit-testing framework Zofu. This library is build together with Greenx when ENABLE_GREENX_UNIT_TESTS=ON:

cmake -DENABLE_GREENX_UNIT_TESTS=ON ../

Unit tests are run with the application tests, using ctest. Simply type ctest in the build directory.

It is also possible to compile Zofu manually. To build Zofu, from GreenX's root (noting that one must define $GX_ROOT):

# building zofu
mkdir external && cd external
git clone https://github.com/acroucher/zofu.git
cd zofu
mkdir build && cd build
cmake \
   -DCMAKE_BUILD_TYPE=release \
   -DCMAKE_INSTALL_PREFIX=${GX_ROOT}/external/zofu/install \
   -DZOFU_FORTRAN_MODULE_INSTALL_DIR:PATH=include \
   ..
make -j 4
make install

# building GreenX 
cd $GX_ROOT 
mkdir build && cd build 
cmake -DENABLE_GREENX_UNIT_TESTS=ON -DZOFU_PATH=${GX_ROOT}/external/zofu/install ../
make -j 2
make install

Again, typing ctest in the GreenX build directory starts the unit tests together with the application tests.

For an example of writing a unit test, see GX-AnalyticContinuation/src/test_pade_approximant.f90. A unit test is a module and follows the naming convention test_MODULENAME.f90. The unit test itself is a module containing subroutines which set up some data, call the routine under test, and make some assertions on the resulting data. Zofu provides the object with which to make the assertions and carry the result. One should write a separate test module for each fortran module they wish to test.

Unit tests are added to the build system straightforwardly:

1. Create a directory in the build folder that will contain the test binary. A good convention is unit_tests/sublibrary_name:

set(UNIT_TEST_DIR "${PROJECT_BINARY_DIR}/unit_tests/analytic-continuation")
file(MAKE_DIRECTORY ${UNIT_TEST_DIR})
message("-- Analytic continuation unit tests written to: ${UNIT_TEST_DIR}")

Noting one is free to choose any name for UNIT_TEST_DIR.

2. Create a list of libraries which your unit tests depend upon. Typically the library associated with that subfolder, for which the module is a part of.

# Libraries on which the unit tests depend
set(LIBS_FOR_UNIT_TESTS LibGXAC)

Noting one is free to choose any name for LIBS_FOR_UNIT_TESTS.

3. Call the function create_unit_test_executable to define the unit test:

create_unit_test_executable(TARGET_TEST_DIR ${UNIT_TEST_DIR}
                            TEST_NAME "test_pade_approximant"
                            REQUIRED_LIBS ${LIBS_FOR_UNIT_TESTS})

For multiple tests, one could call create_unit_test_executable in a loop over a list of modules.