diff --git a/compute.py b/compute.py
index f639e35..aef23cc 100644
--- a/compute.py
+++ b/compute.py
@@ -697,8 +697,6 @@ def run_from_config(config, out_dir=None):
     global GRAVITY_FIELD, GRAVITY_INTERACTION, ELASTIC_FORCE, DAMPING_FORCE, GRAVITY_STRENGTH
     global DRIVING_FORCE, DRIVER_DATA
 
-    global use_marker
-    ...
     box_a = float(config.get("box_a", 10.0))
     raw_alpha = config.get("alpha", 0.2)
     if isinstance(raw_alpha, (list, tuple)):
diff --git a/dynamics.py b/dynamics.py
index b2919cc..a6d59f3 100644
--- a/dynamics.py
+++ b/dynamics.py
@@ -238,7 +238,8 @@ def run_case(config_path, runtime_base, input_dir="input", output_dir="output",
                 # 外部引擎写完整 trajectory.txt，后续抽帧
                 traj_x, traj_y, traj_z, traj_vx, traj_vy, traj_vz = compute.run_engine(
                     engine, input_dir_abs, output_dir_abs, config)
-                compute.save_trajectory_txt(traj_x, traj_y, traj_z, traj_vx, traj_vy, traj_vz, str(runtime_base))
+                if int(config.get("save_trajectory", 0)):
+                    compute.save_trajectory_txt(traj_x, traj_y, traj_z, traj_vx, traj_vy, traj_vz, str(runtime_base))
 
             _elapsed = _time.time() - _t0
             print(f"[run] 引擎: {engine}  计算完成: {record_steps} 步  {_elapsed:.3f} s")
@@ -309,6 +310,16 @@ def run_case(config_path, runtime_base, input_dir="input", output_dir="output",
                 header_fields=hf)
             print(f"[run] 从 trajectory.txt 抽帧生成 display.txt ({n_frames} 帧)")
 
+        # 外部引擎：save_trajectory=0 时清理 trajectory.txt
+        save_traj = int(config.get("save_trajectory", 0))
+        if engine != "python" and not save_traj:
+            traj_path = os.path.join(output_dir_abs, "trajectory.txt")
+            try:
+                os.remove(traj_path)
+                print(f"[run] save_trajectory=0，已删除 {traj_path}")
+            except OSError:
+                pass
+
         # 4. 绘图（可选）
         if not no_plot and config.get("step_plot", 1):
             try:
diff --git a/examples/case06/input/bond.txt b/examples/case06/input/bond.txt
index f3b4d21..2a14f8d 100644
--- a/examples/case06/input/bond.txt
+++ b/examples/case06/input/bond.txt
@@ -1,2 +1,2 @@
 bond_name k rest_length
-k1 1.0 1.0
+k1 10.0 1.0
diff --git a/examples/case06/input/input.txt b/examples/case06/input/input.txt
index 95cbaf0..fa039e5 100644
--- a/examples/case06/input/input.txt
+++ b/examples/case06/input/input.txt
@@ -72,7 +72,7 @@ T_total:  100.0
 NSTEP: 100
 
 # ── 时间步长 ──────────────────────────────────
-DT:    0.01         # 时间步长 (s)
+DT:    0.001         # 时间步长 (s)
 
 # 抽帧范围：只保存 [sample_start, sample_end) 区间内的帧
 sample_start: null        # null 表示从头开始（帧索引从 0 起）