Fix eig_occ.txt lifecycle (#7771)

* fix eig occ txt write mode

* update test

* update to make check pass

Author: MoseyQAQ

interfaces/ASE_interface/abacuslite/io/latestio.py

@@ -443,9 +443,6 @@ def read_abacus_out(fileobj,
 
     # read the eigenvalues (nframe, nk, nbnd)
     elecstate = read_band_from_eig_occ(fileobj.parent / 'eig_occ.txt')
-    # FIXME: remove thw following line till the eig_occ.txt is not written 
-    #        in the append mode
-    (fileobj.parent / 'eig_occ.txt').unlink()
 
     # read the atomic forces (nframe, nat, 3)
     forces = read_forces_from_running_log(abacus_lines)
@@ -701,7 +698,7 @@ def test_read_pw_symm0_nspin4_gamma_md(self):
 
         # remove the files
         (self.testfiles / 'running_md.log').unlink()
-        # (self.testfiles / 'eig_occ.txt').unlink()
+        (self.testfiles / 'eig_occ.txt').unlink()
         (self.testfiles / 'MD_dump').unlink()
 
     def test_read_iter_header_from_running_log(self):

source/source_io/module_energy/write_eig_occ.cpp

@@ -212,8 +212,11 @@ void ModuleIO::write_eig_file(const ModuleBase::matrix &ekb,
     if (GlobalV::MY_RANK == 0)
     {
         std::ofstream ofs_eig0;
+        const auto& inp = PARAM.inp;
+        const bool append = istep > 0
+                            || (inp.calculation == "md" && inp.mdp.md_restart);
 
-		if(PARAM.inp.out_app_flag==true)
+		if (append)
 		{
 			ofs_eig0.open(filename.c_str(), std::ios::app);
 		}

source/source_io/test/write_eig_occ_test.cpp

@@ -97,9 +97,14 @@ TEST_F(IstateInfoTest, OutIstateInfoS1)
         ++i;
     }
 
-    // write eigenvalues and occupations
-    const int istep_in = -1;
-    ModuleIO::write_eig_file(ekb, wg, *kv, istep_in);
+    {
+        std::ofstream stale_file("eig_occ.txt");
+        stale_file << "stale calculation" << std::endl;
+    }
+
+    // A new calculation truncates stale output, then later ionic steps append.
+    ModuleIO::write_eig_file(ekb, wg, *kv, 0);
+    ModuleIO::write_eig_file(ekb, wg, *kv, 1);
 
     // check the output files
     std::ifstream ifs;
@@ -108,7 +113,11 @@ TEST_F(IstateInfoTest, OutIstateInfoS1)
     EXPECT_THAT(str, testing::HasSubstr("Electronic state energy (eV) and occupations"));
     EXPECT_THAT(str, testing::HasSubstr("spin=1 k-point=1/10 Cartesian=0.0000000 0.0000000 0.0000000 (299 plane wave)"));
     EXPECT_THAT(str, testing::HasSubstr("1 2.040854700000000 0.000000000000000"));
+    EXPECT_THAT(str, testing::Not(testing::HasSubstr("stale calculation")));
+    EXPECT_THAT(str, testing::HasSubstr("1     # ionic step"));
+    EXPECT_THAT(str, testing::HasSubstr("2     # ionic step"));
     ifs.close();
+
     remove("eig_occ.txt");
 }