Skip neighbor folding at first call

There may be issues due to the fact that the NL is initialized
with the LAMMPS data file, that does not have to be the same
as the starting config in i-PI

src/MISC/fix_ipi.cpp

@@ -188,6 +188,7 @@ FixIPI::FixIPI(LAMMPS *lmp, int narg, char **arg) : Fix(lmp, narg, arg), irregul
   master = (comm->me == 0) ? 1 : 0;
   inet = 1;
   reset_flag = 0;
+  firsttime = 1;
 
   int iarg = 5;
   while (iarg < narg) {
@@ -253,6 +254,7 @@ void FixIPI::init()
     ipisock = 0;
   // TODO: should check for success in socket opening,
   // but the current open_socket routine dies brutally if unsuccessful
+
   // tell lammps we have assigned a socket
   socketflag = 1;
 
@@ -382,7 +384,11 @@ void FixIPI::initial_integrate(int /*vflag*/)
   // snapshot at neighbor list creation, minimizing the
   // number of neighbor list updates
   auto xhold = neighbor->get_xhold();
-  if (xhold != NULL) { // don't wrap if xhold is not used in the NL
+  if (xhold != NULL && !firsttime) {
+    // don't wrap if xhold is not used in the NL, or the
+    // first call (because the NL is initialized from the
+    // data file that might have nothing to do with the
+    // current structure
     for (int i = 0; i < nlocal; i++) {
       if (mask[i] & groupbit) {
         auto delx = x[i][0] - xhold[i][0];
@@ -397,6 +403,7 @@ void FixIPI::initial_integrate(int /*vflag*/)
       }
     }
   }
+  firsttime = 0;
 
   // check if kspace solver is used
   if (reset_flag && kspace_flag) {

src/MISC/fix_ipi.h

@@ -42,6 +42,7 @@ class FixIPI : public Fix {
   long bsize;
   int kspace_flag;
   int reset_flag;
+  int firsttime;
 
  private:
   class Irregular *irregular;