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# 3.9. Notes for building LAMMPS on Windows¶

## 3.9.1. General remarks¶

LAMMPS is developed and tested primarily on Linux machines. The vast majority of HPC clusters and supercomputers today run on Linux as well. While portability to other platforms is desired, it is not always achieved. That is sometimes due to non-portable code in LAMMPS itself, but more often due to portability limitations of external libraries and tools required to build a specific feature or package. The LAMMPS developers are dependent on LAMMPS users giving feedback and providing assistance in resolving portability issues. This is particularly true for compiling LAMMPS on Windows, since this platform has significant differences in some low-level functionality. As of LAMMPS version 14 December 2021, large parts of LAMMPS can be compiled natively with the Microsoft Visual C++ Compilers. As of LAMMPS version 31 May 2022, also the Intel oneAPI compilers can compile large parts of LAMMPS natively on Windows. This is mostly facilitated by using the Platform abstraction functions in the platform namespace and CMake.

Before trying to build LAMMPS on Windows yourself, please consider the pre-compiled Windows installer packages and see if they are sufficient for your needs.

## 3.9.2. Running Linux on Windows¶

If it is necessary for you to compile LAMMPS on a Windows machine (e.g. because it is your main desktop), please also consider using a virtual machine software and compile and run LAMMPS in a Linux virtual machine, or - if you have a sufficiently up-to-date Windows 10 or Windows 11 installation - consider using the Windows subsystem for Linux. This optional Windows feature allows you to run the bash shell of a Linux system (Ubuntu by default) from within Windows and from there on, you can pretty much use that shell like you are running on a regular Ubuntu Linux machine (e.g. installing software via apt-get and more). For more details on that, please see this tutorial.

## 3.9.3. Using a GNU GCC ported to Windows¶

One option for compiling LAMMPS on Windows natively is to install a Bash shell, Unix shell utilities, Perl, Python, GNU make, and a GNU compiler ported to Windows. The Cygwin package provides a unix/linux interface to low-level Windows functions, so LAMMPS can be compiled on Windows. The necessary (minor) modifications to LAMMPS are included, but may not always up-to-date for recently added functionality and the corresponding new code. A machine makefile for using cygwin for the old build system is provided. Using CMake for this mode of compilation is untested and not likely to work.

When compiling for Windows do not set the -DLAMMPS_MEMALIGN define in the LMP_INC makefile variable and add -lwsock32 -lpsapi to the linker flags in LIB makefile variable. Try adding -static-libgcc or -static or both to the linker flags when your resulting LAMMPS Windows executable complains about missing .dll files. The CMake configuration should set this up automatically, but is untested.

In case of problems, you are recommended to contact somebody with experience in using Cygwin. If you do come across portability problems requiring changes to the LAMMPS source code, or figure out corrections yourself, please report them on the LAMMPS forum at MatSci, or file them as an issue or pull request on the LAMMPS GitHub project.

## 3.9.4. Using Microsoft Visual Studio¶

Following the integration of the platform namespace into the LAMMPS code base, portability of LAMMPS for native compilation on Windows using Visual Studio has been significantly improved. This has been tested with Visual Studio 2019 (aka version 16) and Visual Studio 2022 (aka version 17). We strongly recommend using Visual Studio 2022 version 17.1 or later. Not all features and packages in LAMMPS are currently supported out of the box, but a preset cmake/presets/windows.cmake is provided that contains the packages that have been compiled successfully so far. You must use the CMake based build procedure, since there is no support for GNU make or the Unix shell utilities required for the GNU make build procedure.

It is possible to use both the integrated CMake support of the Visual Studio IDE or use an external CMake installation (e.g. downloaded from cmake.org) to create build files and compile LAMMPS from the command line.

Compilation via command line and unit tests are checked automatically for the LAMMPS development branch through GitHub Actions.

Note

Versions of Visual Studio before version 17.1 may scan the entire LAMMPS source tree and likely miss the correct master CMakeLists.txt and get confused since there are multiple files of that name in different folders but none in top level folder.

Please note, that for either approach CMake will create a so-called “multi-configuration” build environment, and the command lines for building and testing LAMMPS must be adjusted accordingly.

The LAMMPS cmake folder contains a CMakeSettings.json file with build configurations for MSVC compilers and the MS provided Clang compiler package in Debug and Release mode.

To support running in parallel you can compile with OpenMP enabled using the OPENMP package or install Microsoft MPI (including the SDK) and compile LAMMPS with MPI enabled.

Note

This is work in progress and you should contact the LAMMPS developers via GitHub or the LAMMPS forum at MatSci, if you have questions or LAMMPS specific problems.

## 3.9.5. Using Intel oneAPI Compilers and Libraries¶

New in version 31May2022.

After installing the Intel oneAPI base toolkit and the HPC toolkit, it is also possible to compile large parts of LAMMPS natively on Windows using Intel compilers. The HPC toolkit provides two sets of C/C++ and Fortran compilers: the so-called “classic” compilers (icl.exe and ifort.exe) and newer, LLVM based compilers (icx.exe and ifx.exe). In addition to the compilers and their dependent modules, also the thread building blocks (TBB) and the math kernel library (MKL) need to be installed. Two presets (cmake/presets/windows-intel-llvm.cmake and cmake/presets/windows-intel-classic.cmake) are provided for selecting the LLVM based or classic compilers, respectively. The preset cmake/presets/windows.cmake enables compatible packages that are not dependent on additional features or libraries. You must use the CMake based build procedure and use Ninja as build tool. For compiling from the command prompt, thus both CMake and Ninja-build binaries must be installed. It is also possible to use Visual Studio, if it is started (devenv.exe) from a command prompt that has the Intel oneAPI compilers enabled. The Visual Studio settings file in the cmake folder contains configurations for both compiler variants in debug and release settings. Those will use the CMake and Ninja binaries bundled with Visual Studio, thus a separate installation is not required.

Known Limitations

In addition to portability issues with several packages and external libraries, the classic Intel compilers are currently not able to compile the googletest libraries and thus enabling the -DENABLE_TESTING option will result in compilation failure. The LLVM based compilers are compatible.

Note

This is work in progress and you should contact the LAMMPS developers via GitHub or the LAMMPS forum at MatSci, if you have questions or LAMMPS specific problems.

## 3.9.6. Using a cross-compiler¶

If you need to provide custom LAMMPS binaries for Windows, but do not need to do the compilation on Windows, please consider using a Linux to Windows cross-compiler. This is how currently the Windows binary packages are created by the LAMMPS developers. Because of that, this is probably the currently best tested and supported way to build LAMMPS executables for Windows. A CMake preset selecting all packages compatible with this cross-compilation build is provided. The GPU package can only be compiled with OpenCL support. To compile with MPI support, a pre-compiled library and the corresponding header files are required. When building with CMake the matching package will be downloaded automatically, but MPI support has to be explicitly enabled with -DBUILD_MPI=on.

Please keep in mind, though, that this only applies to compiling LAMMPS. Whether the resulting binaries do work correctly is rarely tested by the LAMMPS developers. We instead rely on the feedback of the users of these pre-compiled LAMMPS packages for Windows. We will try to resolve issues to the best of our abilities if we become aware of them. However this is subject to time constraints and focus on HPC platforms.