fix(pair-tab): validate uniform distance grid to avoid silently wrong potentials

deepmd/utils/pair_tab.py

@@ -61,6 +61,15 @@ def reinit(self, filename: str, rcut: float | None = None) -> None:
         self.rmin = self.vdata[0][0]
         self.rmax = self.vdata[-1][0]
         self.hh = self.vdata[1][0] - self.vdata[0][0]
+        dx = np.diff(self.vdata[:, 0])
+        if not np.allclose(dx, self.hh, rtol=1e-5, atol=1e-8):
+            raise ValueError(
+                f"The distance grid in the pairwise table {filename} is not "
+                "evenly spaced. The tabulated potential must be provided on a "
+                "uniform grid, but the stride inferred from the first two rows "
+                f"({self.hh}) does not match all distance intervals. Please "
+                "regrid the table to use a constant distance step."
+            )
         ncol = self.vdata.shape[1] - 1
         n0 = (-1 + np.sqrt(1 + 8 * ncol)) * 0.5
         self.ntypes = int(n0 + 0.1)

source/tests/common/dpmodel/test_pairtab_preprocess.py

@@ -275,5 +275,35 @@ def test_preprocess(self) -> None:
         )
 
 
+class TestPairTabGridSpacing(unittest.TestCase):
+    @patch("numpy.loadtxt")
+    def test_non_uniform_grid(self, mock_loadtxt) -> None:
+        mock_loadtxt.return_value = np.array(
+            [
+                [0.00, 1.0],
+                [0.01, 0.8],
+                [0.02, 0.6],
+                [0.09, 0.3],
+                [0.16, 0.0],
+            ]
+        )
+        with self.assertRaisesRegex(ValueError, "evenly spaced"):
+            PairTab(filename="dummy_path", rcut=0.16)
+
+    @patch("numpy.loadtxt")
+    def test_uniform_grid(self, mock_loadtxt) -> None:
+        mock_loadtxt.return_value = np.array(
+            [
+                [0.00, 1.0],
+                [0.01, 0.8],
+                [0.02, 0.6],
+                [0.03, 0.3],
+                [0.04, 0.0],
+            ]
+        )
+        tab = PairTab(filename="dummy_path", rcut=0.04)
+        np.testing.assert_allclose(tab.hh, 0.01)
+
+
 if __name__ == "__main__":
     unittest.main(warnings="ignore")