Working shift command for merge

src/subroutines.f90

@@ -249,4 +249,23 @@ module subroutines
       end do      
      
     end subroutine siftdown
+
+
+    subroutine apply_periodic(r)
+        !This function checks if an atom is outside the box and wraps it back in. This is generally used when some 
+        !kind of displacement is applied but the simulation cell is desired to be maintained as the same size.
+
+        real(kind=dp), dimension(3), intent(inout) :: r
+
+        integer :: j 
+
+        do j = 1, 3
+            if (r(j) > box_bd(2*j)) then 
+                r(j) = r(j) - box_bd(2*j)
+            else if (r(j) < box_bd(2*j-1)) then 
+                r(j) = r(j) + box_bd(2*j-1)
+            end if
+        end do
+    end subroutine
+
 end module subroutines