Sample LAMMPS MD wrapper on VASP quantum DFT via client/server coupling See the MESSAGE package (doc/Section_messages.html#MESSAGE) and Section_howto.html#howto10 for more details on how client/server coupling works in LAMMPS. In this dir, the vasp_wrap.py is a wrapper on the VASP quantum DFT code so it can work as a "server" code which LAMMPS drives as a "client" code to perform ab initio MD. LAMMPS performs the MD timestepping, sends VASP a current set of coordinates each timestep, VASP computes forces and energy and virial and returns that info to LAMMPS. Messages are exchanged between MC and LAMMPS via a client/server library (CSlib), which is included in the LAMMPS distribution in lib/message. As explained below you can choose to exchange data between the two programs either via files or sockets (ZMQ). If the vasp_wrap.py program became parallel, or the CSlib library calls were integrated into VASP directly, then data could also be exchanged via MPI. ---------------- Build LAMMPS with its MESSAGE package installed: cd lammps/lib/message python Install.py -m -z # build CSlib with MPI and ZMQ support cd lammps/src make yes-message make mpi You can leave off the -z if you do not have ZMQ on your system. ---------------- Prepare to use VASP and the vasp_wrapper.py script You can run the vasp_wrap.py script as-is to test that the coupling between it and LAMMPS is functional. This will use the included vasprun.xml file output by a previous VASP run. But note that the as-is version of vasp_wrap.py will not attempt to run VASP. To do this, you must edit the 1st vaspcmd line at the top of vasp_wrapper.py to be the launch command needed to run VASP on your system. It can be a command to run VASP in serial or in parallel, e.g. an mpirun command. Then comment out the 2nd vaspcmd line immediately following it. Insure you have the necessary VASP input files in this directory, suitable for the VASP calculation you want to perform: INCAR KPOINTS POSCAR_template POTCAR Examples of all but the POTCAR file are provided. As explained below, POSCAR_W is an input file for a 2-atom unit cell of tungsten and can be used to test the LAMMPS/VASP coupling. The POTCAR file is a proprietary VASP file, so use one from your VASP installation. Note that the POSCAR_template file should be matched to the LAMMPS input script (# of atoms and atom types, box size, etc). The provided POSCAR_W matches in.client.W. Once you run VASP yourself, the vasprun.xml file will be overwritten. NOTE: explain how vasp_wrapper.py finds the cslib.py wrapper on the CSlib to import. ---------------- To run in client/server mode: Both the client (LAMMPS) and server (vasp_wrap.py) must use the same messaging mode, namely file or zmq. This is an argument to the vasp_wrap.py code; it can be selected by setting the "mode" variable when you run LAMMPS. The default mode = file. Here we assume LAMMPS was built to run in parallel, and the MESSAGE package was installed with socket (ZMQ) support. This means either of the messaging modes can be used and LAMMPS can be run in serial or parallel. The vasp_wrap.py code is always run in serial, but it launches VASP from Python via an mpirun command which can run VASP itself in parallel. When you run, the server should print out thermodynamic info every timestep which corresponds to the forces and virial computed by VASP. VASP will also generate output files each timestep. The vasp_wrapper.py script could be generalized to archive these. The examples below are commands you should use in two different terminal windows. The order of the two commands (client or server launch) does not matter. You can run them both in the same window if you append a "&" character to the first one to run it in the background. -------------- File mode of messaging: % mpirun -np 1 lmp_mpi -v mode file < in.client.W % python vasp_wrap.py file POSCAR_W % mpirun -np 2 lmp_mpi -v mode file < in.client.W % python vasp_wrap.py file POSCAR_W ZMQ mode of messaging: % mpirun -np 1 lmp_mpi -v mode zmq < in.client.W % python vasp_wrap.py zmq POSCAR_W % mpirun -np 2 lmp_mpi -v mode zmq < in.client.W % python vasp_wrap.py zmq POSCAR_W