Feature: EXX PW supports a ecut different from ecutrho

docs/advanced/input_files/input-main.md

@@ -302,6 +302,9 @@
   - [Exact Exchange (PW)](#exact-exchange-pw)
     - [exxace](#exxace)
     - [exx\_gamma\_extrapolation](#exx_gamma_extrapolation)
+    - [ecutexx](#ecutexx)
+    - [exx_thr_type](#exx_thr_type)
+    - [exx_ene_thr](#exx_ene_thr)
   - [Molecular Dynamics](#molecular-dynamics)
     - [md\_type](#md_type)
     - [md\_nstep](#md_nstep)
@@ -3101,6 +3104,26 @@ These variables are relevant when using hybrid functionals with *[basis_type](#b
 - **Description**: Whether to use the gamma point extrapolation method to calculate the Fock exchange operator. See [https://doi.org/10.1103/PhysRevB.79.205114](https://doi.org/10.1103/PhysRevB.79.205114) for details. Should be set to true most of the time.
 - **Default**: True
 
+### ecutexx
+- **Type**: Real
+- **Description**: The energy cutoff for EXX (Fock) exchange operator in plane wave basis calculations. Reducing `ecutexx` below `ecutrho` may significantly accelerate EXX computations. This speed improvement comes with a reduced numerical accuracy in the exchange energy calculation.
+- **Default**: same as *[ecutrho](#ecutrho)*
+- **Unit**: Ry
+
+### exx_thr_type
+- **Type**: String
+- **Description**: The type of threshold used to judge whether the outer loop has converged in the separate loop EXX calculation.
+  - energy: use the change of exact exchange energy to judge convergence.
+  - density: if the change of charge density difference between two successive outer loop iterations is seen as converged according to *[scf_thr](#scf_thr)*, then the outer loop is seen as converged.
+- **Default**: `density`
+
+### exx_ene_thr
+- **Type**: Real
+- **Availability**: *[exx_thr_type](#exx_thr_type)*==`energy`
+- **Description**: The threshold for the change of exact exchange energy to judge convergence of the outer loop in the separate loop EXX calculation.
+- **Default**: 1e-5
+- **Unit**: Ry
+
 ## Molecular dynamics
 
 These variables are used to control molecular dynamics calculations. For more information, please refer to [md.md](../md.md#molecular-dynamics) in detail.

source/source_io/module_parameter/input_parameter.h

@@ -656,6 +656,7 @@ struct Input_para
     bool exx_gamma_extrapolation = true; // gamma point extrapolation for exx, https://doi.org/10.1103/PhysRevB.79.205114
     std::string exx_thr_type = "density"; // threshold type for exx outer loop, energy or density
     double exx_ene_thr = 1e-5; // threshold for exx outer loop when exx_thr_type = energy
+    double ecutexx = 0.0; // energy cutoff for exx calculation, Ry
 
     // ====   #Parameters (23.XC external parameterization) ========
     /*

source/source_io/read_input_item_other.cpp

@@ -571,6 +571,18 @@ void ReadInput::item_others()
         };
         this->add_item(item);
     }
+    {
+        Input_Item item("ecutexx");
+        item.annotation = "energy cutoff for exx calculation, Ry";
+        read_sync_double(input.ecutexx);
+        item.check_value = [](const Input_Item& item, const Parameter& para) {
+            if (para.input.ecutexx < 0)
+            {
+                ModuleBase::WARNING_QUIT("ReadInput", "ecutexx must >= 0");
+            }
+        };
+        this->add_item(item);
+    }
 
 }
 } // namespace ModuleIO

source/source_pw/module_pwdft/operator_pw/op_exx_pw.cpp

@@ -76,15 +76,22 @@ OperatorEXXPW<T, Device>::OperatorEXXPW(const int* isk_in,
     tpiba = ucell->tpiba;
     Real tpiba2 = tpiba * tpiba;
 
+    // initialize rhopw_dev
+    double ecut_exx = PARAM.inp.ecutexx;
+    if (ecut_exx == 0.0)
+    {
+        ecut_exx = PARAM.inp.ecutrho;
+    }
+
     rhopw_dev = new ModulePW::PW_Basis(wfcpw->get_device(), rhopw->get_precision());
     rhopw_dev->fft_bundle.setfft(wfcpw->get_device(), rhopw->get_precision());
 #ifdef __MPI
     rhopw_dev->initmpi(rhopw->poolnproc, rhopw->poolrank, rhopw->pool_world);
 #endif
     // here we can actually use different ecut to init the grids
-    rhopw_dev->initgrids(rhopw->lat0, rhopw->latvec, rhopw->gridecut_lat * rhopw->tpiba2);
+    rhopw_dev->initgrids(rhopw->lat0, rhopw->latvec, ecut_exx);
     rhopw_dev->initgrids(rhopw->lat0, rhopw->latvec, rhopw->nx, rhopw->ny, rhopw->nz);
-    rhopw_dev->initparameters(rhopw->gamma_only, rhopw->ggecut * rhopw->tpiba2, rhopw->distribution_type, rhopw->xprime);
+    rhopw_dev->initparameters(rhopw->gamma_only, ecut_exx, rhopw->distribution_type, rhopw->xprime);
     rhopw_dev->setuptransform();
     rhopw_dev->collect_local_pw();