style: unify code indentation to 4-space in source_md files

- Replace tabs with 4 spaces in md_func.cpp (lines 198-209)
- Replace tabs with 4 spaces in md_base.cpp (line 65)
- Replace tabs with 4 spaces in run_md.cpp (lines 59-61)

Author: abacus_fixer

source/source_md/md_base.cpp

@@ -62,7 +62,7 @@ void MD_base::setup(ModuleESolver::ESolver* p_esolver, const std::string& global
 
     // mohan add 2026-01-04
     const int stress_step = 0;
-	const int force_step = 0;
+    const int force_step = 0;
     const int istep_print = step_ + step_rst_ + 1;
 
 	ModuleIO::print_screen(stress_step, force_step, istep_print);

source/source_md/md_func.cpp

@@ -195,18 +195,18 @@ void init_vel(const UnitCell& unit_in,
     ModuleBase::Vector3<int> frozen;
     get_mass_mbl(unit_in, allmass, frozen, ionmbl);
     frozen_freedom = frozen.x + frozen.y + frozen.z;
-	if (frozen.x == 0)
-	{
-		++frozen_freedom;
-	}
-	if (frozen.y == 0)
-	{
-		++frozen_freedom;
-	}
-	if (frozen.z == 0)
-	{
-		++frozen_freedom;
-	}
+    if (frozen.x == 0)
+    {
+        ++frozen_freedom;
+    }
+    if (frozen.y == 0)
+    {
+        ++frozen_freedom;
+    }
+    if (frozen.z == 0)
+    {
+        ++frozen_freedom;
+    }
 
     if (unit_in.init_vel)
     {

source/source_md/run_md.cpp

@@ -56,8 +56,8 @@ void md_line(UnitCell& unit_in, ModuleESolver::ESolver* p_esolver, const Paramet
         }
         else
         {
-			// mohan add 2026-01-04
-			const int stress_step = 0;
+            // mohan add 2026-01-04
+            const int stress_step = 0;
             const int force_step = 0;
             const int istep_print = mdrun->step_ + mdrun->step_rst_ + 1;
             ModuleIO::print_screen(stress_step, force_step, istep_print);