units and doc changes

doc/src/fix_client_md.txt

@@ -44,10 +44,11 @@ running {ab initio} MD with quantum forces.
 
 The group associated with this fix is ignored.
 
-The protocol for message format and content that LAMMPS exchanges with
-the server code is defined on the "server md"_server_md.html doc page.
+The protocol and "units"_units.html for message format and content
+that LAMMPS exchanges with the server code is defined on the "server
+md"_server_md.html doc page.
 
-Note that when using LAMMPS in this mode, your LAMMPS input script
+Note that when using LAMMPS as an MD client, your LAMMPS input script
 should not normally contain force field commands, like a
 "pair_style"_doc/pair_style.html, "bond_style"_doc/bond_style.html, or
 "kspace_style"_kspace_style.html commmand.  However it is possible for

doc/src/server_mc.txt

@@ -37,6 +37,7 @@ signals when it is done sending messages to LAMMPS, at which point the
 loop will exit, and the remainder of the LAMMPS script will be
 processed.
 
+The "server"_server.html doc page gives other options for using LAMMPS
 See an example of how this command is used in
 examples/COUPLE/lammps_mc/in.server.
 

doc/src/server_md.txt

@@ -37,7 +37,8 @@ signals when it is done sending messages to LAMMPS, at which point the
 loop will exit, and the remainder of the LAMMPS script will be
 processed.
 
-See an example of how this command is used in
+The "server"_server.html doc page gives other options for using LAMMPS
+in server mode.  See an example of how this command is used in
 examples/message/in.message.server.
 
 :line
@@ -45,13 +46,13 @@ examples/message/in.message.server.
 When using this command, LAMMPS (as the server code) receives the
 current coordinates of all particles from the client code each
 timestep, computes their interaction, and returns the energy, forces,
-and virial for the interacting particles to the client code, so it can
-complete the timestep.  This command could also be used with a client
-code that performs energy minimization, using the server to compute
-forces and energy each iteration of its minimizer.
+and pressure for the interacting particles to the client code, so it
+can complete the timestep.  This command could also be used with a
+client code that performs energy minimization, using the server to
+compute forces and energy each iteration of its minimizer.
 
 When using the "fix client/md" command, LAMMPS (as the client code)
-does the timestepping and receives needed energy, forces, and virial
+does the timestepping and receives needed energy, forces, and pressure
 values from the server code.
 
 The format and content of the exchanged messages are explained here in
@@ -70,7 +71,7 @@ The following pseudo-code uses these values, defined as enums.
 
 enum{SETUP=1,STEP};
 enum{DIM=1,PERIODICITY,ORIGIN,BOX,NATOMS,NTYPES,TYPES,COORDS,UNITS,CHARGE};
-enum{FORCES=1,ENERGY,VIRIAL,ERROR}; :pre
+enum{FORCES=1,ENERGY,PRESSURE,ERROR}; :pre
 
 [Client sends 2 kinds of messages]:
 
@@ -101,11 +102,35 @@ cs->pack(BOX,9,box)            # 3 edge vectors of simulation box
 
 [Server replies to either kind of message]:
 
+# required fields: FORCES, ENERGY, PRESSURE
+# optional fields: ERROR :pre
+
 cs->send(msgID,nfields)      # msgID with nfields
 cs->pack(FORCES,3*Natoms,f)  # vector of 3N forces on atoms
 cs->pack(ENERGY,1,poteng)    # total potential energy of system
-cs->pack(VIRIAL,6,virial)    # global virial tensor (6-vector)
-cs->pack(ERROR,6,virial)     # server had an error (e.g. DFT non-convergence) :pre
+cs->pack(PRESSURE,6,press)   # global pressure tensor (6-vector)
+cs->pack_int(ERROR,flag)     # server had an error (e.g. DFT non-convergence) :pre
+
+:line
+
+The units for various quantities that are sent and received iva
+messages are defined for atomic-scale simulations in the table below.
+The client and server codes (including LAMMPS) can use internal units
+different than these (e.g. "real units"_units.html in LAMMPS), so long
+as they convert to these units for meesaging.
+
+COORDS, ORIGIN, BOX = Angstroms
+CHARGE = multiple of electron charge (1.0 is a proton)
+ENERGY = eV
+FORCES = eV/Angstrom
+PRESSURE = bars :ul
+
+Note that these are "metal units"_units.html in LAMMPS.
+
+If you wish to run LAMMPS in another its non-atomic units, e.g. "lj
+units"_units.html, then the client and server should exchange a UNITS
+message as indicated above, and both the client and server should
+agree on the units for the data they exchange.
 
 :line