Adding virial support

dlext/include/FixDLExt.h

@@ -19,6 +19,7 @@ namespace dlext
 
 using TimeStep = bigint;  // bigint depends on how LAMMPS was built
 using DLExtCallback = std::function<void(TimeStep)>;
+using DLExtSetVirial = std::function<void(double*)>;
 
 // } // Aliases
 
@@ -39,9 +40,11 @@ class DEFAULT_VISIBILITY FixDLExt : public Fix {
     int setmask() override;
     void post_force(int) override;
     void set_callback(DLExtCallback& cb);
+    void set_virial_callback(DLExtSetVirial& cb);
 
 private:
     DLExtCallback callback = [](TimeStep) { };
+    DLExtSetVirial setVirial = [](double*) { };
 };
 
 void register_FixDLExt(LAMMPS* lmp);

dlext/src/FixDLExt.cpp

@@ -32,6 +32,10 @@ FixDLExt::FixDLExt(LAMMPS* lmp, int narg, char** arg)
     if (atom->map_style != Atom::MAP_ARRAY)
         error->all(FLERR, "Fix dlext requires to map atoms as arrays");
 
+    // signal that this fix contributes to the global virial
+    virial_global_flag = 1;
+    thermo_virial = 1;
+
     kokkosable = has_kokkos_cuda_enabled(lmp);
     atomKK = dynamic_cast<AtomKokkos*>(atom);
     execution_space = (on_host || !kokkosable) ? kOnHost : kOnDevice;
@@ -40,9 +44,21 @@ FixDLExt::FixDLExt(LAMMPS* lmp, int narg, char** arg)
 }
 
 int FixDLExt::setmask() { return FixConst::POST_FORCE; }
-void FixDLExt::post_force(int) { callback(update->ntimestep); }
+void FixDLExt::post_force(int vflag) 
+{
+    // virial setup
+    v_init(vflag);
+
+    // invoke callback
+    callback(update->ntimestep);
+
+    // put the virial from the bias into this fix's member variable virial[6] (see fix.h)
+    setVirial(virial);
+}
 void FixDLExt::set_callback(DLExtCallback& cb) { callback = cb; }
 
+void FixDLExt::set_virial_callback(DLExtSetVirial& cb) { setVirial = cb; }
+
 void register_FixDLExt(LAMMPS* lmp)
 {
     auto fix_map = lmp->modify->fix_map;

python/lammps_dlext.cpp

@@ -49,6 +49,7 @@ void export_FixDLExt(py::module& m)
             return static_cast<FixDLExt*>(fix);
         }))
         .def("set_callback", &FixDLExt::set_callback)
+        .def("set_virial_callback", &FixDLExt::set_virial_callback)
         ;
 }