small tweaks

doc/src/lepton_expression.rst

@@ -91,7 +91,10 @@ is exactly equivalent to
 
 The definition of an intermediate value may itself involve other
 intermediate values. Whitespace and quotation characters ('\'' and '"')
-are ignored.  All uses of a value must appear *before* that value’s
+are ignored.  All uses of a value must appear *before* that value's
 definition.  For efficiency reasons, the expression string is parsed,
 optimized, and then stored in an internal, pre-parsed representation for
 evaluation.
+
+Evaluating Lepton expressions is typically between 2 and 4 times
+slower than the corresponding compiled and optimized C++ code.

src/LEPTON/pair_lepton.cpp

@@ -188,8 +188,7 @@ void PairLepton::allocate()
 
 void PairLepton::settings(int narg, char **arg)
 {
-  if (narg != 1) error->all(FLERR, "Illegal pair_style command");
-
+  if (narg != 1) error->all(FLERR, "Incorrect number of arguments for pair_style lepton command");
   cut_global = utils::numeric(FLERR, arg[0], false, lmp);
 }