Sample Monte Carlo (MC) wrapper on LAMMPS 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 mc.cpp/h files are a standalone "client" MC code.  It
should be run on a single processor, though it could become a parallel
program at some point.  LAMMPS is also run as a standalone executable
as a "server" on as many processors as desired using its "server mc"
command; see it's doc page for details.

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 MC
program became parallel, data could also be exchanged via MPI.

The MC code makes simple MC moves, by displacing a single random atom
by a small random amount.  It uses LAMMPS to calculate the energy
change, and to run dynamics between MC moves.

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Build LAMMPS with its MESSAGE package installed:

See the Build extras doc page and its MESSAGE package
section for details.

CMake:

-D PKG_MESSAGE=yes      # include the MESSAGE package
-D MESSAGE_ZMQ=value    # build with ZeroMQ support, value = no (default) or yes

Traditional make:

% 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.

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Build the MC client code

The source files for the MC code are in this dir.  It links with the
CSlib library in lib/message/cslib.

You must first build the CSlib in serial mode, e.g.

% cd lammps/lib/message/cslib/src
% make lib            # build serial and parallel lib with ZMQ support
% make lib zmq=no     # build serial and parallel lib without ZMQ support

Then edit the Makefile in this dir.  The CSLIB variable should be the
path to where the LAMMPS lib/message/cslib/src dir is on your system.
If you built the CSlib without ZMQ support you will also need to
comment/uncomment one line.  Then you can just type

% make

and you should get an "mc" executable.

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To run in client/server mode:

Both the client (MC) and server (LAMMPS) must use the same messaging
mode, namely file or zmq.  This is an argument to the MC 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 MC code is always run in serial.

When you run, the server should print out thermodynamic info
for every MD run it performs (between MC moves).  The client
will print nothing until the simulation ends, then it will
print stats about the accepted MC moves.

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.

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File mode of messaging:

% mpirun -np 1 mc in.mc file tmp.couple
% mpirun -np 1 lmp_mpi -v mode file < in.mc.server

% mpirun -np 1 mc in.mc file tmp.couple
% mpirun -np 4 lmp_mpi -v mode file < in.mc.server

ZMQ mode of messaging:

% mpirun -np 1 mc in.mc zmq localhost:5555
% mpirun -np 1 lmp_mpi -v mode zmq < in.mc.server

% mpirun -np 1 mc in.mc zmq localhost:5555
% mpirun -np 4 lmp_mpi -v mode zmq < in.mc.server

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The input script for the MC program is in.mc.  You can edit it to run
longer simulations.

500   nsteps = total # of steps of MD
100   ndynamics = # of MD steps between MC moves
0.1   delta = displacement size of MC move
1.0   temperature = used in MC Boltzman factor
12345 seed = random number seed

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The problem size that LAMMPS is computing the MC energy for and
running dynamics on is set by the x,y,z variables in the LAMMPS
in.mc.server script.  The default size is 500 particles.  You can
adjust the size as follows:

lmp_mpi -v x 10 -v y 10 -v z 20    # 8000 particles
