feat(pw): expose the serial basis assembly as PW_Basis::init_serial

source/source_basis/module_pw/pw_basis.h

@@ -97,6 +97,22 @@ class PW_Basis
         const bool xprime_in = true
     );
 
+    //Serial basis assembly: the plain production sequence (initgrids ->
+    //initparameters -> default FFT mode -> setuptransform -> collect_local_pw)
+    //without any parallel/device context (no initmpi, default distribution).
+    //NOTE: this no-initmpi use requires the PW sources to be compiled
+    //without __MPI -- with __MPI the initgrids overloads reduce over this
+    //object's communicator, which is MPI_COMM_NULL on a fresh basis that
+    //never called initmpi. The reusable form of the setup chain for serial
+    //utilities and unit tests (compiled with __MPI disabled, like the DFPT
+    //serial test targets); the parallel production path stays in
+    //setup_pwrho.
+    void init_serial(
+        const double lat0_in, //unit length (unit in bohr)
+        const ModuleBase::Matrix3 latvec_in, // Unitcell lattice vectors (unit in lat0)
+        const double gridecut //unit in Ry, ecut to set up grids
+    );
+
     //Set parameters about full planewave, only used in OFDFT for now.
     void setfullpw(
         const bool inpt_full_pw = false,

source/source_basis/module_pw/pw_basis_k.cpp

@@ -529,4 +529,20 @@ double* PW_Basis_K::get_gk2_data() const
     return this->d_gk2;
 }
 
+void PW_Basis_K::init_serial(const double lat0_in,
+                             const ModuleBase::Matrix3 latvec_in,
+                             const int nx_in,
+                             const int ny_in,
+                             const int nz_in,
+                             const double ecut_in,
+                             const int nk_in,
+                             const ModuleBase::Vector3<double>* kvec_d)
+{
+    initgrids(lat0_in, latvec_in, nx_in, ny_in, nz_in);
+    initparameters(false, ecut_in, nk_in, kvec_d);
+    this->fft_bundle.initfftmode(0);
+    setuptransform();
+    collect_local_pw();
+}
+
 } // namespace ModulePW

source/source_basis/module_pw/pw_basis_k.h

@@ -70,6 +70,27 @@ class PW_Basis_K : public PW_Basis
         const bool xprime_in = true
     );
 
+    //Serial basis assembly on a given FFT box (usually the rho grid's
+    //nx/ny/nz so the two bases share the box): initgrids -> initparameters
+    //with the k list -> default FFT mode -> setuptransform ->
+    //collect_local_pw, without any parallel/device context. NOTE: this
+    //no-initmpi use requires the PW sources to be compiled without __MPI
+    //-- with __MPI the initgrids overloads reduce over this object's
+    //communicator, which is MPI_COMM_NULL on a fresh basis that never
+    //called initmpi. The reusable form of the setup chain for serial
+    //utilities and unit tests (compiled with __MPI disabled, like the
+    //DFPT serial test targets); the parallel production path stays in
+    //setup_pwwfc.
+    void init_serial(
+        const double lat0_in,
+        const ModuleBase::Matrix3 latvec_in,
+        const int nx_in,
+        const int ny_in,
+        const int nz_in,
+        const double ecut_in,
+        const int nk_in,
+        const ModuleBase::Vector3<double>* kvec_d);
+
   public:
     int nks=0;//number of k points in this pool
     ModuleBase::Vector3<double> *kvec_d=nullptr; // Direct coordinates of k points

source/source_basis/module_pw/pw_init.cpp

@@ -235,13 +235,26 @@ void PW_Basis:: initparameters(
 
     this->ggecut = pwecut_in / this->tpiba2;
     //ggecut should be no larger than gridecut
-    if(this->ggecut > this->gridecut_lat) 
+    if(this->ggecut > this->gridecut_lat)
     {
         this->ggecut = this->gridecut_lat;
     }
     this->distribution_type = distribution_type_in;
 }
 
+void PW_Basis:: init_serial(
+    const double lat0_in,
+    const ModuleBase::Matrix3 latvec_in,
+    const double gridecut
+)
+{
+    initgrids(lat0_in, latvec_in, gridecut);
+    initparameters(false, gridecut);
+    this->fft_bundle.initfftmode(0);
+    setuptransform();
+    collect_local_pw();
+}
+
 // Set parameters about full planewave, used only in OFDFT for now. sunliang added 2022-08-30
 void PW_Basis::setfullpw(
     const bool inpt_full_pw,

source/source_pw/module_dfpt/test_serial/dfpt_serial_fixture.cpp

@@ -38,18 +38,12 @@ void DFPTSerialBase::SetupBases(const ModuleBase::Vector3<double>& k_d,
                                 int nbands)
 {
     G_ = ucell_.G;
-    pw_rho_.initgrids(lat0_, latvec_, rho_mult_ * ecutwfc_);
-    pw_rho_.initparameters(false, rho_mult_ * ecutwfc_);
-    pw_rho_.fft_bundle.initfftmode(0);
-    pw_rho_.setuptransform();
-    pw_rho_.collect_local_pw();
-
+    // the serial assembly chains live in the PW_Basis / PW_Basis_K
+    // sources (init_serial); this fixture only supplies the geometry
+    // and the (k, q) data
+    pw_rho_.init_serial(lat0_, latvec_, rho_mult_ * ecutwfc_);
     const ModuleBase::Vector3<double> klist[1] = {k_d};
-    pw_wfc_.initgrids(lat0_, latvec_, pw_rho_.nx, pw_rho_.ny, pw_rho_.nz);
-    pw_wfc_.initparameters(false, ecutwfc_, 1, klist);
-    pw_wfc_.fft_bundle.initfftmode(0);
-    pw_wfc_.setuptransform();
-    pw_wfc_.collect_local_pw();
+    pw_wfc_.init_serial(lat0_, latvec_, pw_rho_.nx, pw_rho_.ny, pw_rho_.nz, ecutwfc_, 1, klist);
 
     qlist_.nkstot = 1;
     qlist_.kvec_d.clear();