Feature: multi-k case support for out_dm=1 (#6181)

* Add WARNING_QUIT when Hexx files not exist in hse restart calculations.

* Add support of multi-k case for out_dm=1.

* Update test and docs.

* Update test.

Author: ErjieWu

docs/advanced/input_files/input-main.md

@@ -1645,10 +1645,13 @@ These variables are used to control the output of properties.
 ### out_dm
 
 - **Type**: Boolean
-- **Availability**: Numerical atomic orbital basis (gamma-only algorithm)
+- **Availability**: Numerical atomic orbital basis
 - **Description**: Whether to output the density matrix of localized orbitals into files in the folder `OUT.${suffix}`. The files are named as:
-  - nspin = 1: SPIN1_DM;
-  - nspin = 2: SPIN1_DM, and SPIN2_DM.
+  - For gamma only case:
+    - nspin = 1: SPIN1_DM;
+    - nspin = 2: SPIN1_DM, and SPIN2_DM.
+  - For multi-k points case:
+    - SPIN\*_K\*_DM, where \* stands for index of spin and kpoints;
 - **Default**: False
 
 ### out_dm1

source/module_hamilt_lcao/hamilt_lcaodft/operator_lcao/op_exx_lcao.hpp

@@ -136,6 +136,11 @@ OperatorEXX<OperatorLCAO<TK, TR>>::OperatorEXX(HS_Matrix_K<TK>* hsk_in,
         {
             // Read HexxR in binary format (old version)
             const std::string file_name_exx_cereal = PARAM.globalv.global_readin_dir + "HexxR_" + std::to_string(GlobalV::MY_RANK);
+            std::ifstream ifs(file_name_exx_cereal, std::ios::binary);
+            if (!ifs)
+            {
+                ModuleBase::WARNING_QUIT("OperatorEXX", "Can't open EXX file < " + file_name_exx_cereal + " >.");
+            }
             if (GlobalC::exx_info.info_ri.real_number)
             {
                 ModuleIO::read_Hexxs_cereal(file_name_exx_cereal, *Hexxd);