diff --git a/src/MDI/fix_mdi_engine.cpp b/src/MDI/fix_mdi_engine_old.cpp
similarity index 95%
rename from src/MDI/fix_mdi_engine.cpp
rename to src/MDI/fix_mdi_engine_old.cpp
index f79f3b9980..55ca7893e5 100644
--- a/src/MDI/fix_mdi_engine.cpp
+++ b/src/MDI/fix_mdi_engine_old.cpp
@@ -16,7 +16,7 @@
    MolSSI Driver Interface (MDI) support for LAMMPS
 ------------------------------------------------------------------------- */
 
-#include "fix_mdi_engine.h"
+#include "fix_mdi_engine_old.h"
 #include "library_mdi.h"
 
 #include "atom.h"
@@ -42,7 +42,7 @@ using namespace FixConst;
 
 /* ---------------------------------------------------------------------- */
 
-FixMDIEngine::FixMDIEngine(LAMMPS *lmp, int narg, char **arg) :
+FixMDIEngineOld::FixMDIEngineOld(LAMMPS *lmp, int narg, char **arg) :
     Fix(lmp, narg, arg), id_pe(nullptr), id_ke(nullptr), pe(nullptr), ke(nullptr)
 {
   if (narg != 3) error->all(FLERR, "Illegal fix mdi command");
@@ -96,7 +96,7 @@ FixMDIEngine::FixMDIEngine(LAMMPS *lmp, int narg, char **arg) :
 
 /* ---------------------------------------------------------------------- */
 
-FixMDIEngine::~FixMDIEngine()
+FixMDIEngineOld::~FixMDIEngineOld()
 {
   delete[] target_command;
   delete[] command;
@@ -111,7 +111,7 @@ FixMDIEngine::~FixMDIEngine()
 
 /* ---------------------------------------------------------------------- */
 
-int FixMDIEngine::setmask()
+int FixMDIEngineOld::setmask()
 {
   int mask = 0;
 
@@ -125,7 +125,7 @@ int FixMDIEngine::setmask()
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::exchange_forces()
+void FixMDIEngineOld::exchange_forces()
 {
   double **f = atom->f;
   const int *const mask = atom->mask;
@@ -144,7 +144,7 @@ void FixMDIEngine::exchange_forces()
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::init()
+void FixMDIEngineOld::init()
 {
   // confirm that two required computes are still available
 
@@ -167,35 +167,35 @@ void FixMDIEngine::init()
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::min_setup(int /* vflag */)
+void FixMDIEngineOld::min_setup(int /* vflag */)
 {
   engine_mode("@FORCES");
 }
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::post_integrate()
+void FixMDIEngineOld::post_integrate()
 {
   engine_mode("@COORDS");
 }
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::min_pre_force(int /* vflag */)
+void FixMDIEngineOld::min_pre_force(int /* vflag */)
 {
   engine_mode("@COORDS");
 }
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::min_post_force(int /* vflag */)
+void FixMDIEngineOld::min_post_force(int /* vflag */)
 {
   engine_mode("@FORCES");
 }
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::post_force(int /* vflag */)
+void FixMDIEngineOld::post_force(int /* vflag */)
 {
   if (most_recent_init == 1)
     engine_mode("@FORCES");
@@ -213,7 +213,7 @@ void FixMDIEngine::post_force(int /* vflag */)
    process a single command from driver
 ---------------------------------------------------------------------- */
 
-int FixMDIEngine::execute_command(const char *command, MDI_Comm mdicomm)
+int FixMDIEngineOld::execute_command(const char *command, MDI_Comm mdicomm)
 {
   // confirm this command is supported at this node
 
@@ -369,7 +369,7 @@ int FixMDIEngine::execute_command(const char *command, MDI_Comm mdicomm)
 
 /* ---------------------------------------------------------------------- */
 
-char *FixMDIEngine::engine_mode(const char *node)
+char *FixMDIEngineOld::engine_mode(const char *node)
 {
   /*
   if (screen)
@@ -426,7 +426,7 @@ char *FixMDIEngine::engine_mode(const char *node)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::receive_coordinates(Error *error)
+void FixMDIEngineOld::receive_coordinates(Error *error)
 {
   // get conversion factor to atomic units
   double posconv;
@@ -484,7 +484,7 @@ void FixMDIEngine::receive_coordinates(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_coordinates(Error *error)
+void FixMDIEngineOld::send_coordinates(Error *error)
 {
   // get conversion factor to atomic units
   double posconv;
@@ -529,7 +529,7 @@ void FixMDIEngine::send_coordinates(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_charges(Error *error)
+void FixMDIEngineOld::send_charges(Error *error)
 {
   double *charges;
   double *charges_reduced;
@@ -558,7 +558,7 @@ void FixMDIEngine::send_charges(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_energy(Error *error)
+void FixMDIEngineOld::send_energy(Error *error)
 {
   // get conversion factor to atomic units
   double energy_conv = 1.0;
@@ -591,7 +591,7 @@ void FixMDIEngine::send_energy(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_pe(Error *error)
+void FixMDIEngineOld::send_pe(Error *error)
 {
   // get conversion factor to atomic units
   double energy_conv;
@@ -617,7 +617,7 @@ void FixMDIEngine::send_pe(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_ke(Error *error)
+void FixMDIEngineOld::send_ke(Error *error)
 {
   // get conversion factor to atomic units
   double energy_conv;
@@ -643,7 +643,7 @@ void FixMDIEngine::send_ke(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_types(Error *error)
+void FixMDIEngineOld::send_types(Error *error)
 {
   int *const type = atom->type;
 
@@ -653,7 +653,7 @@ void FixMDIEngine::send_types(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_labels(Error *error)
+void FixMDIEngineOld::send_labels(Error *error)
 {
   char *labels = new char[atom->natoms * MDI_LABEL_LENGTH];
   memset(labels, ' ', atom->natoms * MDI_LABEL_LENGTH);
@@ -672,7 +672,7 @@ void FixMDIEngine::send_labels(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_masses(Error *error)
+void FixMDIEngineOld::send_masses(Error *error)
 {
   double *const rmass = atom->rmass;
   double *const mass = atom->mass;
@@ -710,7 +710,7 @@ void FixMDIEngine::send_masses(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_forces(Error *error)
+void FixMDIEngineOld::send_forces(Error *error)
 {
   // get conversion factor to atomic units
   double force_conv;
@@ -798,7 +798,7 @@ void FixMDIEngine::send_forces(Error *error)
 //    mode = 0: replace current forces with forces from driver
 //    mode = 1: add forces from driver to current forces
 
-void FixMDIEngine::receive_forces(Error *error, int mode)
+void FixMDIEngineOld::receive_forces(Error *error, int mode)
 {
   // get conversion factor to atomic units
   double force_conv;
@@ -847,7 +847,7 @@ void FixMDIEngine::receive_forces(Error *error, int mode)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_cell(Error *error)
+void FixMDIEngineOld::send_cell(Error *error)
 {
   double angstrom_to_bohr;
   MDI_Conversion_factor("angstrom", "bohr", &angstrom_to_bohr);
@@ -875,7 +875,7 @@ void FixMDIEngine::send_cell(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::receive_cell(Error *error)
+void FixMDIEngineOld::receive_cell(Error *error)
 {
   double celldata[9];
 
@@ -911,7 +911,7 @@ void FixMDIEngine::receive_cell(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::send_celldispl(Error *error)
+void FixMDIEngineOld::send_celldispl(Error *error)
 {
   double angstrom_to_bohr;
   MDI_Conversion_factor("angstrom", "bohr", &angstrom_to_bohr);
@@ -933,7 +933,7 @@ void FixMDIEngine::send_celldispl(Error *error)
 
 /* ---------------------------------------------------------------------- */
 
-void FixMDIEngine::receive_celldispl(Error *error)
+void FixMDIEngineOld::receive_celldispl(Error *error)
 {
   // receive the cell displacement from the driver
   double celldata[3];
diff --git a/src/MDI/fix_mdi_engine.h b/src/MDI/fix_mdi_engine_old.h
similarity index 94%
rename from src/MDI/fix_mdi_engine.h
rename to src/MDI/fix_mdi_engine_old.h
index e3d6b37772..4fc87999a0 100644
--- a/src/MDI/fix_mdi_engine.h
+++ b/src/MDI/fix_mdi_engine_old.h
@@ -13,22 +13,22 @@
 
 #ifdef FIX_CLASS
 // clang-format off
-FixStyle(mdi/engine, FixMDIEngine);
+FixStyle(mdi/engine/old, FixMDIEngineOld);
 // clang-format on
 #else
 
-#ifndef LMP_FIX_MDI_ENGINE_H
-#define LMP_FIX_MDI_ENGINE_H
+#ifndef LMP_FIX_MDI_ENGINE_OLD_H
+#define LMP_FIX_MDI_ENGINE_OLD_H
 
 #include "fix.h"
 #include "mdi.h"
 
 namespace LAMMPS_NS {
 
-class FixMDIEngine : public Fix {
+class FixMDIEngineOld : public Fix {
  public:
-  FixMDIEngine(class LAMMPS *, int, char **);
-  ~FixMDIEngine();
+  FixMDIEngineOld(class LAMMPS *, int, char **);
+  ~FixMDIEngineOld();
   int setmask();
   void init();
 
diff --git a/src/MDI/library_mdi.cpp b/src/MDI/library_mdi.cpp
index 5d4992e2b6..d5489207a4 100644
--- a/src/MDI/library_mdi.cpp
+++ b/src/MDI/library_mdi.cpp
@@ -23,7 +23,7 @@
 #define LAMMPS_LIB_MPI 1
 #include "library.h"
 
-#include "fix_mdi_engine.h"
+#include "fix_mdi_engine_old.h"
 
 #include <cstring>
 
@@ -122,9 +122,9 @@ The function executes a single command from an external MDI driver.
 
 int lammps_execute_mdi_command(const char *command, MDI_Comm comm, void *class_obj)
 {
-  FixMDIEngine *mdi_fix = (FixMDIEngine *) class_obj;
+  FixMDIEngineOld *mdi_fix = (FixMDIEngineOld *) class_obj;
   return mdi_fix->execute_command(command, comm);
 
-  // MDIEngine2 *mdi_engine = (MDIEngine2 *) class_obj;
-  // return mdi_engine->execute_command(command, comm);
+  //MDIEngine2 *mdi_engine = (MDIEngine2 *) class_obj;
+  //return mdi_engine->execute_command(command, comm);
 }
diff --git a/src/MDI/mdi_engine.cpp b/src/MDI/mdi_engine_old.cpp
similarity index 96%
rename from src/MDI/mdi_engine.cpp
rename to src/MDI/mdi_engine_old.cpp
index 9bd9258dfc..2c60830b6a 100644
--- a/src/MDI/mdi_engine.cpp
+++ b/src/MDI/mdi_engine_old.cpp
@@ -16,11 +16,11 @@
    MolSSI Driver Interface (MDI) support for LAMMPS
 ------------------------------------------------------------------------- */
 
-#include "mdi_engine.h"
+#include "mdi_engine_old.h"
 
 #include "atom.h"
 #include "error.h"
-#include "fix_mdi_engine.h"
+#include "fix_mdi_engine_old.h"
 #include "force.h"
 #include "mdi.h"
 #include "min.h"
@@ -43,7 +43,7 @@ using namespace LAMMPS_NS;
    when EXIT command is received, mdi/engine command exits
 ---------------------------------------------------------------------- */
 
-void MDIEngine::command(int narg, char ** /*arg*/)
+void MDIEngineOld::command(int narg, char ** /*arg*/)
 {
   // list of nodes and commands that a MDI-compliant MD code should support
 
@@ -178,17 +178,17 @@ void MDIEngine::command(int narg, char ** /*arg*/)
 
   // if the mdi/engine fix is not already present, add it now
 
-  int ifix = modify->find_fix_by_style("mdi/engine");
+  int ifix = modify->find_fix_by_style("mdi/engine/old");
   bool added_mdi_engine_fix = false;
   if (ifix < 0) {
-    modify->add_fix("MDI_ENGINE_INTERNAL all mdi/engine");
+    modify->add_fix("MDI_ENGINE_INTERNAL all mdi/engine/old");
     added_mdi_engine_fix = true;
   }
 
   // identify the mdi_engine fix
 
-  ifix = modify->find_fix_by_style("mdi/engine");
-  mdi_fix = static_cast<FixMDIEngine *>(modify->fix[ifix]);
+  ifix = modify->find_fix_by_style("mdi/engine/old");
+  mdi_fix = static_cast<FixMDIEngineOld *>(modify->fix[ifix]);
 
   // check that LAMMPS is setup as a compatible MDI engine
 
@@ -235,7 +235,7 @@ void MDIEngine::command(int narg, char ** /*arg*/)
    run an MD simulation under control of driver
 ---------------------------------------------------------------------- */
 
-char *MDIEngine::mdi_md()
+char *MDIEngineOld::mdi_md()
 {
   // initialize an MD simulation
 
@@ -293,7 +293,7 @@ char *MDIEngine::mdi_md()
    perform minimization under control of driver
 ---------------------------------------------------------------------- */
 
-char *MDIEngine::mdi_optg()
+char *MDIEngineOld::mdi_optg()
 {
 
   // setup the minimizer in a way that ensures optimization
diff --git a/src/MDI/mdi_engine.h b/src/MDI/mdi_engine_old.h
similarity index 82%
rename from src/MDI/mdi_engine.h
rename to src/MDI/mdi_engine_old.h
index f282714097..bea4574e61 100644
--- a/src/MDI/mdi_engine.h
+++ b/src/MDI/mdi_engine_old.h
@@ -13,25 +13,25 @@
 
 #ifdef COMMAND_CLASS
 // clang-format off
-CommandStyle(mdi/engine, MDIEngine);
+CommandStyle(mdi/engine, MDIEngineOld);
 // clang-format on
 #else
 
-#ifndef LMP_MDI_ENGINE_H
-#define LMP_MDI_ENGINE_H
+#ifndef LMP_MDI_ENGINE_OLD_H
+#define LMP_MDI_ENGINE_OLD_H
 
 #include "command.h"
 
 namespace LAMMPS_NS {
 
-class MDIEngine : public Command {
+class MDIEngineOld : public Command {
  public:
-  MDIEngine(LAMMPS *lmp) : Command(lmp) {}
-  virtual ~MDIEngine() {}
+  MDIEngineOld(LAMMPS *lmp) : Command(lmp) {}
+  virtual ~MDIEngineOld() {}
   void command(int, char **);
 
  private:
-  class FixMDIEngine *mdi_fix;
+  class FixMDIEngineOld *mdi_fix;
 
   char *mdi_md();
   char *mdi_optg();