minor grammar correction

Author: simongravelle

lammps-tutorials.tex

@@ -3425,7 +3425,7 @@ \subsubsection{Adding water}
 
 \paragraph{Using hydrid potentials}
 
-The first particularly of our system is that it combine water and
+The first particularly of our system is that it combines water and
 silica, which necessitates the use of two force fields: Vashishta (for
 $\text{SiO}_2$), and TIP4P (for water).  Here, the TIP4P/2005 model is
 employed for the water~\cite{abascal2005general}.  Open the