Fix: remove .bak file, update comments and warnings in module_dh

source/source_io/module_ctrl/ctrl_scf_lcao.cpp

@@ -1,6 +1,7 @@
 #include "ctrl_scf_lcao.h" // use ctrl_scf_lcao()
 
 #include "source_base/formatter.h"
+#include "source_base/tool_quit.h" // use ModuleBase::WARNING_QUIT
 #include "source_estate/elecstate_lcao.h" // use elecstate::ElecState
 #include "source_hamilt/hamilt.h"         // use Hamilt<T>
 #include "source_lcao/hamilt_lcao.h"      // use hamilt::HamiltLCAO<TK, TR>
@@ -55,7 +56,15 @@ void setup_exx_dh_params<double>(ModuleIO::WriteDHParams& dh_params, Exx_NAO<dou
 
 template <typename TK>
 void setup_exx_h_params(ModuleIO::WriteHParams& h_params, Exx_NAO<TK>& exx_nao)
-{}
+{
+    // Only the gamma-only (TK==double) specialization below actually writes V^EXX(R).
+    // This generic body is instantiated for the multi-k (TK==std::complex) path, where the
+    // EXX-H output is unsupported. Reject it explicitly here so the request cannot be silently
+    // dropped (the WARNING_QUIT inside write_h_exx is unreachable at multi-k).
+    ModuleBase::WARNING_QUIT("setup_exx_h_params",
+                             "out_mat_h_exx is only supported for gamma-only: the V^EXX(R) "
+                             "output is not available at multi-k. Use gamma_only.");
+}
 
 template <>
 void setup_exx_h_params<double>(ModuleIO::WriteHParams& h_params, Exx_NAO<double>& exx_nao)

source/source_io/module_dhs/write_dH.cpp

@@ -8,6 +8,9 @@
 #include "source_io/module_parameter/parameter.h"
 #include "source_lcao/module_hcontainer/hcontainer_funcs.h"
 #include "source_lcao/module_hcontainer/output_hcontainer.h"
+#ifdef __EXX
+#include "source_hamilt/module_xc/exx_info.h"
+#endif
 
 #include <algorithm>
 #include <complex>
@@ -138,6 +141,20 @@ void write_dH_components(WriteDHParams& params)
                                  "nspin=4 (noncollinear) yet; only nspin=1 and nspin=2.");
     }
 
+#ifdef __EXX
+    // The EXX interfaces carried by WriteDHParams are gamma-only (see write_dH.h): at multi-k
+    // dH^EXX would be the derivative with respect to every mirror atom, which this output is
+    // not meant for. Quit instead of writing a dH sum that silently omits the EXX term.
+    if (GlobalC::exx_info.info_global.cal_exx && !PARAM.globalv.gamma_only_local
+        && (PARAM.inp.out_mat_dh[0] || PARAM.inp.out_mat_dh_exx[0]))
+    {
+        ModuleBase::WARNING_QUIT("write_dH_components",
+                                 "out_mat_dh (the dH sum) and out_mat_dh_exx are only supported for gamma-only when EXX is on. "
+                                 "Use gamma_only, or request the individual non-EXX terms (out_mat_dh_t, "
+                                 "out_mat_dh_vnl, out_mat_dh_vl, out_mat_dh_vh, out_mat_dh_vxc).");
+    }
+#endif
+
     GlobalV::ofs_running << " >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>" << std::endl;
     GlobalV::ofs_running << " |                                                                    |" << std::endl;
     GlobalV::ofs_running << " |                 #Print out dH/dR components#                       |" << std::endl;

source/source_io/module_dhs/write_dH.h

@@ -54,8 +54,15 @@ struct WriteDHParams
     std::vector<const hamilt::HContainer<double>*> dmR;
     const Charge* chg = nullptr; // ground-state charge for XC Hellmann-Feynman (FDM)
 #ifdef __EXX
-    // gamma (TK==double) exx interfaces used by write_dH_exx; exactly one is set depending on
-    // GlobalC::exx_info.info_ri.real_number (exd: real Hexx, exc: complex Hexx).
+    // The gamma-only (TK==double) exx interfaces used by write_dH_exx. 
+    // Deliberately NOT templated on TK, for two reasons:
+    //   1. Physics: at multi-k the derivative would be taken with respect to every mirror
+    //      atom of the periodic images, which is not what this output is used for.
+    //   2. Cost: templating these pointers on TK would force WriteHParams, WriteDHParams and
+    //      every free function taking them to become templates as well -- a large, purely
+    //      mechanical change for a case nobody needs.
+    // Multi-k + EXX is therefore rejected up front (see write_dH_components)
+    // instead of silently producing output with the EXX term missing.
     Exx_LRI_Interface<double, double>* exd = nullptr;
     Exx_LRI_Interface<double, std::complex<double>>* exc = nullptr;
 #endif

source/source_io/module_hs/write_H_terms.cpp

@@ -411,6 +411,8 @@ void write_h_exx(WriteHParams& params)
     ModuleBase::TITLE("ModuleIO", "write_h_exx");
     ModuleBase::timer::start("ModuleIO", "write_h_exx");
 
+    // Multi-k out_mat_h_exx is rejected upstream at the call site (setup_exx_h_params in
+    // ctrl_scf_lcao.cpp); this function is only reached on the gamma-only path.
     const UnitCell& ucell = *params.ucell;
     const Parallel_Orbitals& pv = *params.pv;
     const K_Vectors& kv = *params.kv;

source/source_io/module_hs/write_H_terms.h

@@ -38,8 +38,12 @@ struct WriteHParams
     int nat = 0;
     bool also_hR = false; // H(k) is always written; H(R) (CSR) only when this is true
 #ifdef __EXX
-    // gamma (TK==double) exx interfaces used by write_h_exx; exactly one is set depending on
-    // GlobalC::exx_info.info_ri.real_number (exd: real Hexx, exc: complex Hexx).
+    // The gamma-only (TK==double) exx interfaces used by write_h_exx. 
+    // Deliberately NOT templated on TK, because it would force WriteHParams, WriteDHParams and
+    //      every free function taking them to become templates as well -- a large, purely
+    //      mechanical change for a case nobody needs.
+    // Multi-k + EXX is therefore rejected up front (see write_h_exx)
+    // instead of silently producing output with the EXX term missing.
     Exx_LRI_Interface<double, double>* exd = nullptr;
     Exx_LRI_Interface<double, std::complex<double>>* exc = nullptr;
 #endif