diff --git a/dpdata/qe/scf.py b/dpdata/qe/scf.py
index f86708605..8c5299d07 100755
--- a/dpdata/qe/scf.py
+++ b/dpdata/qe/scf.py
@@ -12,47 +12,67 @@
 kbar2evperang3 = 1e3 / 1.602176621e6
 
 
-def get_block(lines, keyword, skip=0):
-    ret = []
-    for idx, ii in enumerate(lines):
-        if keyword in ii:
-            blk_idx = idx + 1 + skip
-            while len(lines[blk_idx]) == 0:
-                blk_idx += 1
-            while len(lines[blk_idx]) != 0 and blk_idx != len(lines):
-                ret.append(lines[blk_idx])
-                blk_idx += 1
+def get_block(lines, start_marker):
+    start_idx = None
+    for idx, line in enumerate(lines):
+        if start_marker in line:
+            start_idx = idx + 1
             break
-    return ret
+    if start_idx is None:
+        raise RuntimeError(f"{start_marker} not found in the input lines.")
+
+    block = []
+    for line in lines[start_idx:]:
+        if line.strip() == "" or line.strip().startswith("&"):
+            break
+        block.append(line.strip())
+    return block
+
+
+def get_block(lines, start_marker, skip=0):
+    start_idx = None
+    for idx, line in enumerate(lines):
+        if start_marker in line:
+            start_idx = idx + 1 + skip
+            break
+    if start_idx is None:
+        raise RuntimeError(f"{start_marker} not found in the input lines.")
+
+    block = []
+    for line in lines[start_idx:]:
+        if line.strip() == "" or line.strip().startswith("&"):
+            break
+        block.append(line.strip())
+    return block
 
 
 def get_cell(lines):
-    ret = []
-    for idx, ii in enumerate(lines):
-        if "ibrav" in ii:
+    for idx, line in enumerate(lines):
+        if "ibrav" in line:
+            ibrav = int(line.replace(",", "").split("=")[-1])
             break
-    blk = lines[idx : idx + 2]
-    ibrav = int(blk[0].replace(",", "").split("=")[-1])
+    else:
+        raise RuntimeError("ibrav not found in the input lines.")
+
     if ibrav == 0:
-        for iline in lines:
-            if "CELL_PARAMETERS" in iline and "angstrom" not in iline.lower():
+        for line in lines:
+            if "CELL_PARAMETERS" in line and "angstrom" not in line.lower():
                 raise RuntimeError(
                     "CELL_PARAMETERS must be written in Angstrom. Other units are not supported yet."
                 )
         blk = get_block(lines, "CELL_PARAMETERS")
-        for ii in blk:
-            ret.append([float(jj) for jj in ii.split()[0:3]])
+        ret = []
+        for line in blk:
+            ret.append([float(value) for value in line.split()[0:3]])
         ret = np.array(ret)
     elif ibrav == 1:
         a = None
-        for iline in lines:
-            line = iline.replace("=", " ").replace(",", "").split()
+        for line in lines:
+            line = line.replace("=", " ").replace(",", "").split()
             if len(line) >= 2 and "a" == line[0]:
-                # print("line = ", line)
                 a = float(line[1])
             if len(line) >= 2 and "celldm(1)" == line[0]:
                 a = float(line[1]) * bohr2ang
-        # print("a = ", a)
         if not a:
             raise RuntimeError("parameter 'a' or 'celldm(1)' cannot be found.")
         ret = np.array([[a, 0.0, 0.0], [0.0, a, 0.0], [0.0, 0.0, a]])