Mention that WHAM version 2.1.0 is required for the "units" option.

Author: akohlmey

lammps-tutorials.tex

@@ -3901,15 +3901,17 @@ \subsubsection{Method 1: Free sampling}
 
 \subsubsection{Method 2: Umbrella sampling}
 
-Umbrella sampling is a biased molecular dynamics method in which additional forces
-are added to a chosen atom to force it to explore the more unfavorable areas of
-the system~\cite{kastner2011umbrella, allen2017computer, frenkel2023understanding}.
-Here, to encourage one of the atoms to explore the central region of the box,
-we apply a potential $V$ and force it to move along the $x$-axis. The chosen path
-is called the axis of reaction. Several simulations (called windows) will be
-conducted with varying positions for the center of the applied biasing. The results
-will be analyzed using the weighted histogram analysis method (WHAM)~\cite{kumar1992weighted,kumar1995multidim},
-which allows for the removal of the biasing effect and ultimately deduces the
+Umbrella sampling is a biased molecular dynamics method in which
+additional forces are added to a chosen atom to force it to explore the
+more unfavorable areas of the system~\cite{kastner2011umbrella,
+  allen2017computer, frenkel2023understanding}.  Here, to encourage one
+of the atoms to explore the central region of the box, we apply a
+potential $V$ and force it to move along the $x$-axis. The chosen path
+is called the axis of reaction. Several simulations (called windows)
+will be conducted with varying positions for the center of the applied
+biasing. The results will be analyzed using the weighted histogram
+analysis method (WHAM)~\cite{kumar1992weighted,kumar1995multidim}, which
+allows for the removal of the biasing effect and ultimately deduces the
 unbiased free energy profile.
 
 \paragraph{LAMMPS input script}
@@ -4038,18 +4040,21 @@ \subsubsection{Method 2: Umbrella sampling}
 WHAM~\cite{kumar1992weighted,kumar1995multidim} algorithm as implemented
 by Marc Grossfield~\cite{grossfieldimplementation}.  You can download it
 from \href{http://membrane.urmc.rochester.edu/?page_id=126}{Alan
-  Grossfield}'s website.  The executable called \flecmd{wham} generated
-by following the instructions from the website must be placed next to
+  Grossfield}'s website.  Make sure you download the WHAM code version
+2.1.0 or later which introduces the \lmpcmd{units} command-line option
+used below. The executable called \flecmd{wham} generated by following
+the instructions from the website must be placed next to
 \flecmd{umbrella-sampling.lmp}.  To apply the WHAM algorithm to our
 simulation, we need a metadata file containing:
 \begin{itemize}
 \item the paths to all the data files,
 \item the values of $x_\text{des}$,
 \item the values of $k$.
 \end{itemize}
-Download the \href{\filepath tutorial7/umbrella-sampling.meta}{\dwlcmd{umbrella-sampling.meta}} file
-and save it next to \flecmd{umbrella-sampling.lmp}.  Then, run the WHAM algorithm
-by typing the following command in the terminal:
+Download the \href{\filepath
+  tutorial7/umbrella-sampling.meta}{\dwlcmd{umbrella-sampling.meta}}
+file and save it next to \flecmd{umbrella-sampling.lmp}.  Then, run the
+WHAM algorithm by typing the following command in the terminal:
 \begin{lstlisting}
 ./wham units real -30 30 50 1e-8 119.8 0 \
     umbrella-sampling.meta umbrella-sampling.dat