Update ase.py: To avoid errors in writing to the .extxyz format from an Atom object coverted from .npy with dpdata. (#717)

Author: ZhouXY-PKU

dpdata/plugins/ase.py

@@ -181,7 +181,17 @@ def to_labeled_system(self, data, *args, **kwargs) -> list[ase.Atoms]:
                 # v_pref = 1 * 1e4 / 1.602176621e6
                 vol = structure.get_volume()
                 # results['stress'] = data["virials"][ii] / (v_pref * vol)
-                results["stress"] = -data["virials"][ii] / vol
+                stress33 = -data["virials"][ii] / vol
+                results["stress"] = np.array(
+                    [
+                        stress33[0][0],
+                        stress33[1][1],
+                        stress33[2][2],
+                        stress33[1][2],
+                        stress33[0][2],
+                        stress33[0][1],
+                    ]
+                )
 
             structure.calc = SinglePointCalculator(structure, **results)
             structures.append(structure)