diff --git a/src/atom.cpp b/src/atom.cpp
index 6578016208..099a5098e6 100644
--- a/src/atom.cpp
+++ b/src/atom.cpp
@@ -270,6 +270,8 @@ void Atom::create_avec(const char *style, int narg, char **arg, char *suffix)
   vfrac_flag = spin_flag = eradius_flag = ervel_flag = erforce_flag = 0;
 
   // create instance of AtomVec
+  // use grow to initialize atom-based arrays to length 1
+  // so that x[0][0] can be referenced even if proc has no atoms
 
   int sflag;
   avec = new_avec(style,suffix,sflag);
diff --git a/src/lammps.cpp b/src/lammps.cpp
index 97376a4951..d191d0c278 100644
--- a/src/lammps.cpp
+++ b/src/lammps.cpp
@@ -449,7 +449,7 @@ LAMMPS::~LAMMPS()
 
 void LAMMPS::create()
 {
-  // Comm class must be created before Atom
+  // Comm class must be created before Atom class
   // so that nthreads is defined when create_avec invokes grow()
 
   if (cuda) comm = new CommCuda(this);
diff --git a/src/respa.cpp b/src/respa.cpp
index 3e08f505d2..b07228134e 100644
--- a/src/respa.cpp
+++ b/src/respa.cpp
@@ -560,6 +560,11 @@ void Respa::recurse(int ilevel)
       timer->stamp(TIME_COMM);
     }
 
+    // force computations
+    // important that ordering is same as Verlet
+    // so that any order dependencies are the same
+    // when potentials are invoked at same level
+
     force_clear(newton[ilevel]);
     if (modify->n_pre_force_respa)
       modify->pre_force_respa(vflag,ilevel,iloop);
diff --git a/src/verlet.cpp b/src/verlet.cpp
index 8e1bccc362..db47a675c6 100644
--- a/src/verlet.cpp
+++ b/src/verlet.cpp
@@ -263,6 +263,9 @@ void Verlet::run(int n)
     }
 
     // force computations
+    // important for pair to come before bonded contributions
+    // since some bonded potentials tally pairwise energy/virial
+    // and Pair:ev_tally() needs to be called before any tallying
 
     force_clear();
     if (n_pre_force) modify->pre_force(vflag);