Displacements: generate periodic displacements on the first call, eve…

…n if the boundary conditions set at the time are not periodic, since that's the current default behavior. If periodic boundary conditions need to be set along some axes only make sure to set them before startup()

src/madness/mra/displacements.h

@@ -159,6 +159,11 @@ namespace madness {
 
 
     public:
+        /// first time this is called displacements are generated.
+        /// if boundary conditions are not periodic, the periodic displacements
+        /// are generated for all axes. If need to use periodic boundary conditions
+        /// for some axes only, make sure to set the boundary conditions appropriately
+        /// before the first call to this
         Displacements() {
           MADNESS_PRAGMA_CLANG(diagnostic push)
           MADNESS_PRAGMA_CLANG(diagnostic ignored "-Wundefined-var-template")
@@ -168,9 +173,11 @@ namespace madness {
           }
 
           if constexpr (NDIM <= 3) {
-            if (disp_periodic[0].empty() && FunctionDefaults<NDIM>::get_bc().is_periodic().any()) {
-              disp_periodic_axes =
-                  FunctionDefaults<NDIM>::get_bc().is_periodic();
+            if (disp_periodic[0].empty()) {
+              if (FunctionDefaults<NDIM>::get_bc().is_periodic().any())
+                disp_periodic_axes = FunctionDefaults<NDIM>::get_bc().is_periodic();
+              else
+                disp_periodic_axes = decltype(disp_periodic_axes){true};
               Level nmax = 8 * sizeof(Translation) - 2;
               for (Level n = 0; n < nmax; ++n)
                 make_disp_periodic(bmax_default(), n);
@@ -187,7 +194,7 @@ namespace madness {
                 if (is_periodic != disp_periodic_axes) {
                   std::string msg =
                       "Displacements<" + std::to_string(NDIM) +
-                      ">::get_disp(level, is_periodic): is_periodic differs from the boundary conditions FunctionDefault's had when Displacements were initialized; on-demand displacements generation is not yet supported";
+                      ">::get_disp(level, is_periodic): is_periodic differs from the boundary conditions FunctionDefault's had when Displacements were initialized; on-demand periodic displacements generation is not yet supported";
                   MADNESS_EXCEPTION(msg.c_str(), 1);
                 }
                 return disp_periodic[n];