This directory has a code that shows how LAMMPS can be linked to a driver application as a library. The purpose is to illustrate how another code could perform computations while using LAMMPS to perform MD, or how an umbrella code or script could call both LAMMPS and some other code to perform a coupled calculation.

Umbrella.cpp is the simple driving code that will call LAMMPS.

LAMMPS must first be built as a library. See the "Making LAMMPS" section of Section_start.html in the documentation for info on how to do this. Basically, you type something like

make makelib make -f Makefile.lib g++

in the LAMMPS src directory to create liblmp_g++.a

You can then build the umbrella code with a compile line something like this, which includes paths to the LAMMPS library interface, MPI, and FFTW.

g++ -I/home/sjplimp/tools/mpich/include -I/home/sjplimp/lammps/src

-L/home/sjplimp/lammps/src -L/home/sjplimp/tools/mpich/lib
-L/home/sjplimp/tools/fftw/lib umbrella.cpp
-llmp_g++ -lfftw -lmpich -o umbrella

You then run umbrella on a parallel machine on some number of processors Q with 2 arguments:

mpirun -np Q umbrella P in.lj

P is the number of procs you want LAMMPS to run on (must be <= Q). In.lj is a LAMMPS input script.

Umbrella will launch LAMMPS on P procs, read the input script a line at a time, and pass each command line to LAMMPS. The final line of the script is a "run" command, so LAMMPS will run the problem.

Umbrella then requests all the atom coordinates from LAMMPS, moves one of the atoms a small amount "epsilon", passes the coordinates back to LAMMPS, and runs LAMMPS again. If you look at the output, you should see a small energy change between runs, due to the moved atom.