NequIP-C/C++-Fortran-interface

Fortran - C/C++ interface for NequIP.

Interface between Fortran, C and the C++ frontend of Pytorch for the NequIP code.

The interface is built following the DeePMD-kit-Fortran-Cpp-interface as well as the LAMMPS interface pair_nequip interface. The plan is to merge the interface to CP2K.

Installation

This interface currently requires:

• Python >= 3.7
• pip3
• cmake >= 3.0.0
• gfortran v>= 11.2.0
• gcc >= 11.2.0

The following installation script will run pip3 install requirements.txt and run cmake:

./install_interface.sh

Running the code

To perform inference with nequip on a 32 water molecules box using the model water-deploy.pth with the Fortran-C/C++ interface and the PyTorch C++ Frontend simply do:

cd nequip_interface
./build/call_nequip_interface_fort

Instead, to do it just with the C/C++ interface and Pytorch C++ Frontend do:

cd nequip_interface
./build/call_nequip_interface

Brief description:

• fortran_call.90 is the main program, where coordinates and species information are defined, and where the water-deploy.pth model is declared and passed to C/C++
• wrap_nequip.f90 contains the Fortran module that is interfaced to C via ISO_C_BINDING
• c_wrapper.cpp and c_wrapper.h are the C/C++ code and header, respectively, for interoperability between C and C++. The header file contains the __cplusplus preprocessor macro and the extern "C" function such that the C++ code has C linkage. c_wrapper.cpp calls nequip.cpp
• nequip.h and nequip.cpp are the C++ code and header containing the NequipPot class that takes care of loading the model and of inference.

TODO:

• write minimal neighbor lists subroutine in Fortran and then pass this list to the C/C++ code to be finally able to perform inference using the compute_nequip function inside nequip_wrapper.cpp. For now the module neighnborlists.f90 only computes distances. This is how it would be done once Nequip is implemented in CP2K.
• add virial term to calculate the stress.

Note:

• Right now I have bypassed the calculation with neighborlist, as the only thing that is required is to do a double loop over atoms to calculate neighbors within a cutoff to get the indixes of the connected atom pairs (edges) and the cell_shifts identifying whether the connection from first to second crosses a periodic boundary.