update command line launch instructions

Author: akohlmey

lammps-tutorials.tex

@@ -4515,27 +4515,38 @@ \subsection{Preferences}
 \end{itemize}
 See Ref.\,\citenum{lammps_gui_docs} for a full list of options.
 
-\section{Running LAMMPS via Command Line}
+\section{Running LAMMPS on the Command Line without the GUI}
 \label{command-line-label}
 
-LAMMPS can be executed from the command line on Linux, macOS,
-as well as Windows.  On Linux/macOS, first navigate to the directory containing
-the \flecmd{input.lmp} file and execute:
-\begin{lstlisting}
+LAMMPS can also be executed from the command line on Linux, macOS, and
+Windows without using the GUI.  This is the more common way to run LAMMPS.
+Both, the \lammpsgui{} program and the LAMMPS command line executable
+utilize the same LAMMPS library and thus no changes to the input file should
+be required.
+
+First open a terminal or command line prompt window and navigate to the
+directory containing the \flecmd{input.lmp} file. Then execute:
+\begin{lstlisting}[language=tcl]
 lmp -in input.lmp
 \end{lstlisting}
-where \flecmd{lmp} is the LAMMPS executable.
-For parallel execution on 4 processors, use:
-\begin{lstlisting}[language=bash]
-mpirun -np 4 lmp -in input.lmp
-\end{lstlisting}
-On Windows, run the following command via Command Prompt or PowerShell:
-\begin{lstlisting}
-lmp.exe -in input.lmp
+where \flecmd{lmp} is the command line LAMMPS command.
+
+For parallel execution with 4 processors (via OpenMP threads where supported
+by the OPENMP package), use:
+\begin{lstlisting}[language=tcl]
+lmp -in input.lmp -pk omp 4 -sf omp
 \end{lstlisting}
-where \flecmd{lmp.exe} is the Windows executable version of LAMMPS.  See
-Ref.\,\citenum{lammps_run_docs} for a complete description on how to run
-LAMMPS.
+
+\begin{note}
+  Running in parallel via MPI requires a correspondingly compiled LAMMPS
+  package and is not compatible with the GUI.  On supercomputers or HPC
+  clusters, pre-compiled LAMMPS executables are often provided by the
+  user support staff.  Please consult the corresponding documentation of
+  the facility or contact its user support for more information.
+\end{note}
+
+See Ref.\,\citenum{lammps_run_docs} for a complete description on how to
+run LAMMPS.
 
 \end{appendices}