deepmodeling · mohanchen · Sep 8, 2026 · Jul 7, 2026 · Jul 9, 2026 · Jul 9, 2026
diff --git a/docs/advanced/input_files/input-main.md b/docs/advanced/input_files/input-main.md
@@ -584,6 +584,7 @@
   - relax: perform structure relaxation calculations, the relax_nmax parameter depicts the maximal number of ionic iterations
   - cell-relax: perform cell relaxation calculations
   - md: perform molecular dynamics simulations
+  - socket: run as a socket client for external drivers using the i-PI protocol
   - get_pchg: obtain partial (band-decomposed) charge densities (for LCAO basis only). See out_pchg for more information
   - get_wf: obtain real space wave functions (for LCAO basis only). See out_wfc_norm and out_wfc_re_im for more information
   - get_s: obtain the overlap matrix formed by localized orbitals (for LCAO basis with multiple k points). the file name is SR.csr with file format being the same as that generated by out_mat_hs2
@@ -840,7 +841,12 @@
 ### chg_extrap
 
 - **Type**: String
-- **Description**: Charge extrapolation method for MD and relaxation calculations.
+- **Description**: Charge extrapolation method for MD, relaxation, and socket-driven calculations.
+
+  When set to default, ABACUS chooses second-order for md, first-order for
+  relax/cell-relax/socket, and atomic for other calculations. Socket-driven
+  molecular dynamics can explicitly set second-order if the external driver
+  updates structures smoothly enough for second-order extrapolation.
 - **Default**: default
 
 ### nb2d

diff --git a/docs/parameters.yaml b/docs/parameters.yaml
@@ -28,6 +28,7 @@ parameters:
       * relax: perform structure relaxation calculations, the relax_nmax parameter depicts the maximal number of ionic iterations
       * cell-relax: perform cell relaxation calculations
       * md: perform molecular dynamics simulations
+      * socket: run as a socket client for external drivers using the i-PI protocol
       * get_pchg: obtain partial (band-decomposed) charge densities (for LCAO basis only). See out_pchg for more information
       * get_wf: obtain real space wave functions (for LCAO basis only). See out_wfc_norm and out_wfc_re_im for more information
       * get_s: obtain the overlap matrix formed by localized orbitals (for LCAO basis with multiple k points). the file name is SR.csr with file format being the same as that generated by out_mat_hs2
@@ -328,7 +329,12 @@ parameters:
     category: System variables
     type: String
     description: |
-      Charge extrapolation method for MD and relaxation calculations.
+      Charge extrapolation method for MD, relaxation, and socket-driven calculations.
+
+      When set to default, ABACUS chooses second-order for md, first-order for
+      relax/cell-relax/socket, and atomic for other calculations. Socket-driven
+      molecular dynamics can explicitly set second-order if the external driver
+      updates structures smoothly enough for second-order extrapolation.
     default_value: default
     unit: ""
     availability: ""

diff --git a/source/source_io/module_parameter/read_input_item_system.cpp b/source/source_io/module_parameter/read_input_item_system.cpp
@@ -75,7 +75,7 @@ void ReadInput::item_system()
     }
     {
         Input_Item item("calculation");
-        item.annotation = "scf; relax; md; cell-relax; nscf; get_s; get_wf; get_pchg; gen_bessel; gen_opt_abfs; test_memory; test_neighbour";
+        item.annotation = "scf; relax; md; socket; cell-relax; nscf; get_s; get_wf; get_pchg; gen_bessel; gen_opt_abfs; test_memory; test_neighbour";
         item.category = "System variables";
         item.type = "String";
         item.description = R"(Specify the type of calculation.
@@ -85,6 +85,7 @@ void ReadInput::item_system()
 * relax: perform structure relaxation calculations, the relax_nmax parameter depicts the maximal number of ionic iterations
 * cell-relax: perform cell relaxation calculations
 * md: perform molecular dynamics simulations
+* socket: run as a socket client for external drivers using the i-PI protocol
 * get_pchg: obtain partial (band-decomposed) charge densities (for LCAO basis only). See out_pchg for more information
 * get_wf: obtain real space wave functions (for LCAO basis only). See out_wfc_norm and out_wfc_re_im for more information
 * get_s: obtain the overlap matrix formed by localized orbitals (for LCAO basis with multiple k points). the file name is SR.csr with file format being the same as that generated by out_mat_hs2
@@ -102,6 +103,7 @@ void ReadInput::item_system()
             std::vector<std::string> callist = {"scf",
                                                 "relax",
                                                 "md",
+                                                "socket",
                                                 "cell-relax",
                                                 "nscf",
                                                 "get_s",
@@ -266,7 +268,7 @@ void ReadInput::item_system()
         item.description = "If set to True, calculate the force at the end of the electronic iteration.";
         item.default_value = "False";
         item.reset_value = [](const Input_Item& item, Parameter& para) {
-            std::vector<std::string> use_force = {"cell-relax", "relax", "md"};
+            std::vector<std::string> use_force = {"cell-relax", "relax", "md", "socket"};
             std::vector<std::string> not_use_force = {"get_wf", "get_pchg", "get_s"};
             if (std::find(use_force.begin(), use_force.end(), para.input.calculation) != use_force.end())
             {
@@ -873,7 +875,12 @@ Available options are:
         item.annotation = "atomic; first-order; second-order; dm:coefficients of SIA";
         item.category = "System variables";
         item.type = "String";
-        item.description = "Charge extrapolation method for MD and relaxation calculations.";
+        item.description = R"(Charge extrapolation method for MD, relaxation, and socket-driven calculations.
+
+When set to default, ABACUS chooses second-order for md, first-order for
+relax/cell-relax/socket, and atomic for other calculations. Socket-driven
+molecular dynamics can explicitly set second-order if the external driver
+updates structures smoothly enough for second-order extrapolation.)";
         item.default_value = "default";
         read_sync_string(input.chg_extrap);
         item.reset_value = [](const Input_Item& item, Parameter& para) {
@@ -882,7 +889,7 @@ Available options are:
                 para.input.chg_extrap = "second-order";
             }
             else if (para.input.chg_extrap == "default"
-                     && (para.input.calculation == "relax" || para.input.calculation == "cell-relax"))
+                     && (para.input.calculation == "relax" || para.input.calculation == "cell-relax" || para.input.calculation == "socket"))
             {
                 para.input.chg_extrap = "first-order";
             }

diff --git a/source/source_io/test_serial/read_input_item_test.cpp b/source/source_io/test_serial/read_input_item_test.cpp
@@ -362,6 +362,11 @@ TEST_F(InputTest, Item_test)
         it->second.reset_value(it->second, param);
         EXPECT_EQ(param.input.chg_extrap, "first-order");
 
+        param.input.chg_extrap = "default";
+        param.input.calculation = "socket";
+        it->second.reset_value(it->second, param);
+        EXPECT_EQ(param.input.chg_extrap, "first-order");
+
         param.input.chg_extrap = "default";
         param.input.calculation = "none";
         it->second.reset_value(it->second, param);

diff --git a/source/source_main/driver_run.cpp b/source/source_main/driver_run.cpp
@@ -59,26 +59,33 @@ void Driver::driver_run()
     unitcell::check_atomic_stru(ucell, PARAM.inp.min_dist_coef);
 
     //! 2: initialize the ESolver (depends on a set-up ucell after `setup_cell`)
+    Input_para socket_esolver_inp = PARAM.inp;
+    const bool socket_mode = (socket_esolver_inp.calculation == "socket");
+    if (socket_mode)
+    {
+        socket_esolver_inp.calculation = "scf";
+    }
+    const Input_para& esolver_inp = socket_mode ? socket_esolver_inp : PARAM.inp;
+
     this->init_hardware();
 
-    ModuleESolver::ESolver* p_esolver = ModuleESolver::init_esolver(PARAM.inp, ucell);
+    ModuleESolver::ESolver* p_esolver = ModuleESolver::init_esolver(esolver_inp, ucell);
 
     //! 3: initialize Esolver and fill json-structure
-    p_esolver->before_all_runners(ucell, PARAM.inp);
+    p_esolver->before_all_runners(ucell, esolver_inp);
 
     // this Json part should be moved to before_all_runners, mohan 2024-05-12
 #ifdef __RAPIDJSON
     Json::gen_stru_wrapper(&ucell);
 #endif
 
-    const std::string cal = PARAM.inp.calculation;
-
     //! 4: different types of calculations
+    const std::string cal = PARAM.inp.calculation;
     if (cal == "md")
     {
         Run_MD::md_line(ucell, p_esolver, PARAM);
     }
-    else if (cal == "scf" || cal == "relax" || cal == "cell-relax" || cal == "nscf")
+    else if (cal == "scf" || cal == "relax" || cal == "cell-relax" || cal == "nscf" || cal == "socket")
     {
         Relax_Driver rl_driver;
         rl_driver.relax_driver(p_esolver, ucell, PARAM.inp, GlobalV::ofs_running);

diff --git a/source/source_relax/CMakeLists.txt b/source/source_relax/CMakeLists.txt
@@ -2,6 +2,8 @@ add_library(
     relax
     OBJECT
     relax_data.cpp
+    ipi_socket.cpp
+    socket_driver.cpp
     cg_base.cpp
     relax_driver.cpp
     relax_sync.cpp