Add semigrand mention.

Author: davidlmobley

paper/basic_training.pdf

@@ -1135,7 +1135,7 @@ \subsubsection{Grid based Ewald summation}
 
 \begin{itemize}
 \item \textbf{Count the cost: } Think about what you know about the timescales of what you want to observe and determine whether it is tractable to simulate this given the size of your system, your computational resources, and the expense of the simulation. Would the questions you want to answer be better addressed a different way?
-\item Pick the desired ensemble ($NVT$, $NPT$, $NVE$, $\mu VT$)
+\item Pick the desired ensemble ($NVT$, $NPT$, $NVE$, $\mu VT$)\footnote{For mixtures, the semi-grand ensemble (or osmotic ensemble) may be of interest, where the number of particles if fixed but their identities can change~\cite{allen_computer_2017} allowing, e.g., a constant chemical potential for salt ions to be maintained~\cite{Ross:2018:J.Phys.Chem.B}}
 \item Determine reference states that you are trying to emulate/discover.
 \item What temperature, pressure, etc. are you interested in?
 \item What force field properly describes your system?