QMCPACK is an open-source production-level many-body ab initio Quantum Monte Carlo code for computing the electronic structure of atoms, molecules, 2D nanomaterials and solids. The solid-state capabilities include metallic systems as well as insulators. QMCPACK is expected to run well on workstations through to the latest generation supercomputers. Besides high performance, particular emphasis is placed on code quality and reproducibility.

Obtain the latest release from https://github.com/QMCPACK/qmcpack/releases or clone the development source from https://github.com/QMCPACK/qmcpack. A full installation guide and steps to perform an initial QMC calculation are given in the extensive online documentation for QMCPACK.

• C++ 17 and C99 capable compilers.
• CMake v3.17.0 or later, build utility, http://www.cmake.org
• BLAS/LAPACK, numerical library. Use vendor and platform-optimized libraries.
• LibXml2, XML parser, http://xmlsoft.org/
• HDF5, portable I/O library, http://www.hdfgroup.org/HDF5/
• BOOST v1.61.0 or newer, peer-reviewed portable C++ source libraries, http://www.boost.org
• FFTW, FFT library, http://www.fftw.org/
• MPI, parallel library. Optional, but a near requirement for production calculations.
• Python3. Older versions are not supported as of January 2020.
• CUDA v11.0 or later. Optional, but required for builds with NVIDIA GPU support.

We aim to support open source compilers and libraries released within two years of each QMCPACK release. Use of software versions over two years old may work but is discouraged and untested. Proprietary compilers (Intel, NVHPC) are generally supported over the same period but may require use of an exact version. We also aim to support the standard software environments on machines such as Summit at OLCF, Theta at ALCF, and Cori at NERSC. Use of the most recently released compilers and library versions is particularly encouraged for highest performance and easiest configuration.

Nightly testing currently includes the following software versions on x86:

• Compilers
  • GCC 11.2.0, 9.2.0
  • Clang/LLVM 13.0.0
  • Intel 19.1.1.217 configured to use C++ library from GCC 9.1.0
  • NVIDIA HPC SDK 21.5 configured to use C++ library from GCC 9.1.0
• Boost 1.77.0, 1.68.0
• HDF5 1.12.1
• FFTW 3.3.10, 3.3.8
• CMake 3.21.1, 3.15.0
• MPI
  • OpenMPI 4.1.1, 3.1.6
  • Intel MPI 19.1.1.217
• CUDA 11.4

Workflow tests are performed with Quantum Espresso v6.8.0 and PySCF v1.7.5. These check trial wavefunction generation and conversion through to actual QMC runs.

On a developmental basis we also check the latest Clang and GCC development versions, AMD AOMP and Intel OneAPI compilers.

The build system for QMCPACK is based on CMake. It will auto-configure based on the detected compilers and libraries. Previously QMCPACK made extensive use of toolchains, but the system has since been updated to eliminate the use of toolchain files for most cases. Specific compile options can be specified either through specific environment or CMake variables. When the libraries are installed in standard locations, e.g., /usr, /usr/local, there is no need to set environment or CMake variables for the packages.

See the manual linked at https://qmcpack.readthedocs.io/en/develop/ and https://www.qmcpack.org/documentation or buildable using sphinx from the sources in docs/. A PDF version is still available at https://qmcpack.readthedocs.io/_/downloads/en/develop/pdf/

If you are feeling lucky and are on a standard UNIX-like system such as a Linux workstation:

• Safest quick build option is to specify the C and C++ compilers through their MPI wrappers. Here we use Intel MPI and Intel compilers. Move to the build directory, run CMake and make

cd build
cmake -DCMAKE_C_COMPILER=mpiicc -DCMAKE_CXX_COMPILER=mpiicpc ..
make -j 8

• Substitute mpicc and mpicxx or other wrapped compiler names to suit your system. e.g. With OpenMPI use

cd build
cmake -DCMAKE_C_COMPILER=mpicc -DCMAKE_CXX_COMPILER=mpicxx ..
make -j 8

• If you are feeling particularly lucky, you can skip the compiler specification:

cd build
cmake ..
make -j 8

The complexities of modern computer hardware and software systems are such that you should check that the auto-configuration system has made good choices and picked optimized libraries and compiler settings before doing significant production. i.e. Check the details below.

A number of environment variables affect the build. In particular, they can control the default paths for libraries, the default compilers, etc. The list of environment variables is given below:

In addition to reading the environment variables, CMake provides a number of optional variables that can be set to control the build and configure steps. When passed to CMake, these variables will take precedent over the environment and default variables. To set them add -D FLAG=VALUE to the configure line between the CMake command and the path to the source directory.

• General build options

    CMAKE_C_COMPILER    Set the C compiler
    CMAKE_CXX_COMPILER  Set the C++ compiler
    CMAKE_BUILD_TYPE    A variable which controls the type of build (defaults to Release).
                        Possible values are:
                        None (Do not set debug/optmize flags, use CMAKE_C_FLAGS or CMAKE_CXX_FLAGS)
                        Debug (create a debug build)
                        Release (create a release/optimized build)
                        RelWithDebInfo (create a release/optimized build with debug info)
                        MinSizeRel (create an executable optimized for size)
    CMAKE_SYSTEM_NAME   Set value to CrayLinuxEnvironment when cross-compiling
                        in Cray Programming Environment.
    CMAKE_C_FLAGS       Set the C flags.  Note: to prevent default debug/release flags
                        from being used, set the CMAKE_BUILD_TYPE=None
                        Also supported: CMAKE_C_FLAGS_DEBUG, CMAKE_C_FLAGS_RELEASE,
                                        CMAKE_C_FLAGS_RELWITHDEBINFO
    CMAKE_CXX_FLAGS     Set the C++ flags.  Note: to prevent default debug/release flags
                        from being used, set the CMAKE_BUILD_TYPE=None
                        Also supported: CMAKE_CXX_FLAGS_DEBUG, CMAKE_CXX_FLAGS_RELEASE,
                                        CMAKE_CXX_FLAGS_RELWITHDEBINFO

• Key QMC build options

     QMC_CUDA            Enable legacy CUDA code path for NVIDIA GPU acceleration (1:yes, 0:no)
     QMC_COMPLEX         Build the complex (general twist/k-point) version (1:yes, 0:no)
     QMC_MIXED_PRECISION Build the mixed precision (mixing double/float) version
                         (1:yes (GPU default), 0:no (CPU default)).
                         The CPU support is experimental.
                         Use float and double for base and full precision.
                         The GPU support is quite mature.
                         Use always double for host side base and full precision
                         and use float and double for CUDA base and full precision.
     ENABLE_CUDA         ON/OFF(default). Enable CUDA code path for NVIDIA GPU acceleration.
                         Production quality for AFQMC. Pre-production quality for real-space.
                         Use CMAKE_CUDA_ARCHITECTURES, default 70, to set the actual GPU architecture.
     ENABLE_OFFLOAD      ON/OFF(default). Experimental feature. Enable OpenMP target offload for GPU acceleration.
     ENABLE_TIMERS       ON(default)/OFF. Enable fine-grained timers. Timers are on by default but at level coarse
                         to avoid potential slowdown in tiny systems.
                         For systems beyond tiny sizes (100+ electrons) there is no risk.

• Additional QMC options

     QE_BIN              Location of Quantum Espresso binaries including pw2qmcpack.x
     RMG_BIN             Location of RMG binary
     QMC_DATA            Specify data directory for QMCPACK performance and integration tests
     QMC_INCLUDE         Add extra include paths
     QMC_EXTRA_LIBS      Add extra link libraries
     QMC_BUILD_STATIC    ON/OFF(default). Add -static flags to build
     QMC_SYMLINK_TEST_FILES Set to zero to require test files to be copied. Avoids space
                            saving default use of symbolic links for test files. Useful
                            if the build is on a separate filesystem from the source, as
                            required on some HPC systems.

• libxml2 related

     LIBXML2_INCLUDE_DIR Include directory for libxml2
     LIBXML2_LIBRARY     Libxml2 library

• HDF5 related

     HDF5_PREFER_PARALLEL 1(default for MPI build)/0, enables/disable parallel HDF5 library searching.
     ENABLE_PHDF5         1(default for parallel HDF5 library)/0, enables/disable parallel collective I/O.

• FFTW related

     FFTW_INCLUDE_DIRS   Specify include directories for FFTW
     FFTW_LIBRARY_DIRS   Specify library directories for FFTW

In the build directory, run cmake with appropriate options, then make.

• Using Intel compilers and their MPI wrappers. Assumes HDF5 and libxml2 will be automatically detected.

cd build
cmake -DCMAKE_C_COMPILER=mpiicc -DCMAKE_CXX_COMPILER=mpiicpc ..
make -j 8

It is recommended to create a helper script that contains the configure line for CMake. This is particularly useful when using environment variables, packages are installed in custom locations, or the configure line may be long or complex. In this case it is recommended to add "rm -rf CMake*" before the configure line to remove existing CMake configure files to ensure a fresh configure each time that the script is called. and example script build.sh is given below:

export CXX=mpic++
export CC=mpicc
export HDF5_ROOT=/opt/hdf5
export BOOST_ROOT=/opt/boost

rm -rf CMake*

cmake                                               \
  -D CMAKE_BUILD_TYPE=Debug                         \
  -D LIBXML2_INCLUDE_DIR=/usr/include/libxml2      \
  -D LIBXML2_LIBRARY=/usr/lib/x86_64-linux-gnu/libxml2.so \
  -D FFTW_INCLUDE_DIRS=/usr/include                 \
  -D FFTW_LIBRARY_DIRS=/usr/lib/x86_64-linux-gnu    \
  -D QMC_DATA=/projects/QMCPACK/qmc-data            \
  ..

Set compile flags manually:

   cmake                                                \
      -D CMAKE_BUILD_TYPE=None                          \
      -D CMAKE_C_COMPILER=mpicc                         \
      -D CMAKE_CXX_COMPILER=mpic++                      \
      -D CMAKE_C_FLAGS="  -O3 -fopenmp -malign-double -fomit-frame-pointer -finline-limit=1000 -fstrict-aliasing -funroll-all-loops -Wno-deprecated -march=native -mtune=native" \
      -D CMAKE_CXX_FLAGS="-O3 -fopenmp -malign-double -fomit-frame-pointer -finline-limit=1000 -fstrict-aliasing -funroll-all-loops -Wno-deprecated -march=native -mtune=native" \
      ..

Add extra include directories:

   cmake                                                \
      -D CMAKE_BUILD_TYPE=Release                       \
      -D CMAKE_C_COMPILER=mpicc                         \
      -D CMAKE_CXX_COMPILER=mpic++                      \
      -D QMC_INCLUDE="~/path1;~/path2"                  \
      ..

We highly encourage tests to be run before using QMCPACK. Details are given in the QMCPACK manual. QMCPACK includes extensive validation tests to ensure the correctness of the code, compilers, tools, and runtime. The tests should ideally be run each compilation, and certainly before any research use. The tests include checks of the output against known mean-field, quantum chemistry, and other QMC results.

While some tests are fully deterministic, due to QMCPACK's stochastic nature some tests are statistical and can occasionally fail. We employ a range of test names and labeling to differentiate between these, as well as developmental tests that are known to fail. In particular, "deterministic" tests include this in their ctest test name, while tests known to be unstable (stochastically or otherwise) are labeled unstable using ctest labels.

The tests currently use up to 16 cores in various combinations of MPI tasks and OpenMP threads. Current status for many combinations of systems, compilers, and libraries can be checked at https://cdash.qmcpack.org

Note that due to the small electron and walker counts used in the tests, they should not be used for any performance measurements. These should be made on problem sizes that are representative of actual research calculations. As described in the manual, performance tests are provided to aid in monitoring performance.

From the build directory, invoke ctest specifying only the unit tests

ctest -R unit

All of these tests should pass.

From the build directory, invoke ctest specifying only tests that are deterministic and known to be reliable.

ctest -R deterministic -LE unstable

These tests currently take a few seconds to run, and include all the unit tests. All tests should pass. Failing tests likely indicate a significant problem that should be solved before using QMCPACK further. This ctest invocation can be used as part of an automated installation verification process.

From the build directory, invoke ctest specifying only tests including "short" to run that are known to be stable.

ctest -R short -LE unstable

These tests currently take up to around one hour. On average, all tests should pass at a three sigma level of reliability. Any initially failing test should pass when rerun.

Individual tests can be run by specifying their name

ctest -R name-of-test-to-run

For more information, consult QMCPACK pages at http://www.qmcpack.org, the manual at https://qmcpack.readthedocs.io/en/develop/index.html, or its sources in the docs directory.

If you have trouble using or building QMCPACK, or have questions about its use, please post to the Google QMCPACK group, create a GitHub issue at https://github.com/QMCPACK/qmcpack/issues or contact a developer.

Contributions of any size are very welcome. Guidance for contributing to QMCPACK is included in Chapter 1 of the manual https://qmcpack.readthedocs.io/en/develop/introduction.html#contributing-to-qmcpack. We use a git flow model including pull request reviews. A continuous integration system runs on pull requests. See https://github.com/QMCPACK/qmcpack/wiki for details. For an extensive contribution, it can be helpful to discuss on the Google QMCPACK group, to create a GitHub issue, or to talk directly with a developer in advance.

Contributions are made under the same UIUC/NCSA open source license that covers QMCPACK. Please contact us if this is problematic.