Repository: duartegroup/autodE (python)

Issue:
DLC backtransform resets dihedral values
Dihedrals should always move by the smaller angle deviation (n +- 2pi). This is done during the DLC ->. Cartesian backtransform, but is reset at the end - causing very large apparent steps in the DLC space. (which will degrade Hessian updates)


Pull request:
Improve DIC to Cartesian transformation
Resolves #346 


***

## Checklist

* [ ] The changes include an associated explanation of how/why
* [ ] Test pass
* [ ] Documentation has been updated
* [ ] Changelog has been updated


Patch:
diff --git a/autode/opt/coordinates/dic.py b/autode/opt/coordinates/dic.py
index 7cf3abd..44d4418 100644
--- a/autode/opt/coordinates/dic.py
+++ b/autode/opt/coordinates/dic.py
@@ -34,7 +34,7 @@ if TYPE_CHECKING:
     from autode.hessians import Hessian
 
 
-MAX_BACK_TRANSFORM_ITERS = 20
+MAX_BACK_TRANSFORM_ITERS = 50
 
 
 class DIC(InternalCoordinates):  # lgtm [py/missing-equals]
@@ -70,8 +70,10 @@ class DIC(InternalCoordinates):  # lgtm [py/missing-equals]
         Returns:
             (np.ndarray): U
         """
-
-        lambd, u = np.linalg.eigh(primitives.G)
+        # calculate spectroscopic G matrix
+        B = primitives.get_B(x)
+        G = np.dot(B, B.T)
+        lambd, u = np.linalg.eigh(G)
 
         # Form a transform matrix from the primitive internals by removing the
         # redundant subspace comprised of small eigenvalues. This forms a set
@@ -124,8 +126,9 @@ class DIC(InternalCoordinates):  # lgtm [py/missing-equals]
 
         dic.U = U  # Transform matrix primitives -> non-redundant
 
-        dic.B = np.matmul(U.T, primitives.B)
+        dic.B = np.matmul(U.T, primitives.get_B(x))
         dic.B_T_inv = np.linalg.pinv(dic.B)
+        dic._q = q.copy()
         dic._x = x.copy()
         dic.primitives = primitives
 
@@ -215,23 +218,46 @@ class DIC(InternalCoordinates):  # lgtm [py/missing-equals]
 
         # Initialise
         s_k, x_k = np.array(self, copy=True), self.to("cartesian").copy()
-        q_init = self.primitives(x_k)
+        q_init = self._q
         x_1 = self.to("cartesian") + np.matmul(self.B_T_inv, value)
 
         success = False
         rms_s = np.inf
+        # NOTE: J. Comput. Chem., 2013, 34, 1842 suggests if step size
+        # is larger than 0.5 bohr (= 0.2 Å), internal step can be halved
+        # for easier convergence (i.e. damp = 1/2)
+        if np.linalg.norm(value) > 0.2:
+            damp = 0.5
+        else:
+            damp = 1.0
+
+        # hybrid SIBT/IBT algorithm
         for i in range(1, MAX_BACK_TRANSFORM_ITERS + 1):
             try:
-                x_k = x_k + np.matmul(self.B_T_inv, (s_new - s_k))
+                x_k = x_k + np.matmul(self.B_T_inv, damp * (s_new - s_k))
 
-                # Rebuild the primitives & DIC from the back-transformed Cartesians
+                # Rebuild the DIC from back-transformed Cartesians
                 q_k = self.primitives.close_to(x_k, q_init)
                 s_k = np.matmul(self.U.T, q_k)
-                self.B = np.matmul(self.U.T, self.primitives.B)
-                self.B_T_inv = np.linalg.pinv(self.B)
 
+                # Rebuild the B matrix every 10 steps
+                if i % 10 == 0:
+                    self.B = np.matmul(self.U.T, self.primitives.get_B(x_k))
+                    self.B_T_inv = np.linalg.pinv(self.B)
+
+                rms_s_old = rms_s
                 rms_s = np.sqrt(np.mean(np.square(s_k - s_new)))
 
+                # almost converged, turn off damping
+                if rms_s < 1e-6:
+                    damp = 1.0
+                # RMS going down, reduce damping
+                elif rms_s < rms_s_old and i > 1:
+                    damp = min(1.2 * damp, 1.0)
+                # RMS going up, increase damping
+                elif rms_s > rms_s_old:
+                    damp = max(0.7 * damp, 0.1)
+
             # for ill-conditioned primitives, there might be math error
             except ArithmeticError:
                 break
@@ -256,11 +282,13 @@ class DIC(InternalCoordinates):  # lgtm [py/missing-equals]
                     "DIC->Cart iterative back-transform did not converge"
                 )
 
-        s_k = np.matmul(self.U.T, self.primitives(x_k))
-        self.B = np.matmul(self.U.T, self.primitives.B)
+        q_k = self.primitives.close_to(x_k, q_init)
+        s_k = np.matmul(self.U.T, q_k)
+        self.B = np.matmul(self.U.T, self.primitives.get_B(x_k))
         self.B_T_inv = np.linalg.pinv(self.B)
 
         self[:] = s_k
+        self._q = q_k
         self._x = x_k
 
         return self
diff --git a/autode/opt/coordinates/internals.py b/autode/opt/coordinates/internals.py
index 421ddf7..d4b608b 100644
--- a/autode/opt/coordinates/internals.py
+++ b/autode/opt/coordinates/internals.py
@@ -48,9 +48,10 @@ class InternalCoordinates(OptCoordinates, ABC):  # lgtm [py/missing-equals]
         arr = super().__new__(cls, input_array, units="Å")
 
         arr._x = None
+        arr._q = None
         arr.primitives = None
 
-        for attr in ("_x", "primitives"):
+        for attr in ("_x", "primitives", "_q"):
             setattr(arr, attr, getattr(input_array, attr, None))
 
         return arr
@@ -59,7 +60,7 @@ class InternalCoordinates(OptCoordinates, ABC):  # lgtm [py/missing-equals]
         """See https://numpy.org/doc/stable/user/basics.subclassing.html"""
         OptCoordinates.__array_finalize__(self, obj)
 
-        for attr in ("_x", "primitives"):
+        for attr in ("_x", "primitives", "_q"):
             setattr(self, attr, getattr(obj, attr, None))
 
         return
@@ -91,8 +92,6 @@ class PIC(list, ABC):
         """
         super().__init__(args)
 
-        self._B: Optional[np.ndarray] = None
-
         if not self._are_all_primitive_coordinates(args):
             raise ValueError(
                 "Cannot construct primitive internal coordinates "
@@ -107,28 +106,11 @@ class PIC(list, ABC):
             super().append(item)
 
     def append(self, item: Primitive) -> None:
-        """Append an item to this set of primitives"""
+        """Appending directly is not allowed, use add() instead"""
         raise NotImplementedError(
             "Please use PIC.add() to add new primitives to the set"
         )
 
-    @property
-    def B(self) -> np.ndarray:
-        """Wilson B matrix"""
-
-        if self._B is None:
-            raise AttributeError(
-                f"{self} had no B matrix. Please calculate "
-                f"the value of the primitives to determine B"
-            )
-
-        return self._B
-
-    @property
-    def G(self) -> np.ndarray:
-        """Spectroscopic G matrix as the symmetrised Wilson B matrix"""
-        return np.dot(self.B, self.B.T)
-
     @classmethod
     def from_cartesian(
         cls,
@@ -146,7 +128,6 @@ class PIC(list, ABC):
         """Populate Primitive-s used in the construction of set"""
 
         q = self._calc_q(x)
-        self._calc_B(x)
 
         return q
 
@@ -160,7 +141,6 @@ class PIC(list, ABC):
         assert len(self) == len(other) and isinstance(other, np.ndarray)
 
         q = self._calc_q(x)
-        self._calc_B(x)
 
         for i, primitive in enumerate(self):
             if isinstance(primitive, PrimitiveDihedralAngle):
@@ -194,7 +174,7 @@ class PIC(list, ABC):
     def _populate_all(self, x: np.ndarray) -> None:
         """Populate primitives from an array of cartesian coordinates"""
 
-    def _calc_B(self, x: np.ndarray) -> None:
+    def get_B(self, x: np.ndarray) -> np.ndarray:
         """Calculate the Wilson B matrix"""
 
         if len(self) == 0:
@@ -210,8 +190,7 @@ class PIC(list, ABC):
         for i, primitive in enumerate(self):
             B[i] = primitive.derivative(x=cart_coords)
 
-        self._B = B
-        return None
+        return B
 
     @staticmethod
     def _are_all_primitive_coordinates(args: tuple) -> bool:
diff --git a/doc/changelog.rst b/doc/changelog.rst
index e91f244..b66d774 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -10,10 +10,11 @@ Functionality improvements
 - Improved constrained optimisation (:code:`CRFOptimiser`) and handling of multiple constraints
 - Adds compatability with numpy v2.0
 - Improved implementation of the RFO-TRM (:code:`QAOptimiser`) optimiser that can handle constraints
+- Added static internal back-transform and damping for faster and easier DIC to Cartesian coordinate transformation
 
 Bug Fixes
 *********
-- ...
+- DIC to Cartesian transform will now always use :code:`PIC.close_to()` to ensure steps along dihedral have the smallest change, even after back-transform is complete
 
 
 1.4.3


Test patch:
diff --git a/tests/test_opt/test_coordiantes.py b/tests/test_opt/test_coordiantes.py
index f9b71ab..a761ea9 100644
--- a/tests/test_opt/test_coordiantes.py
+++ b/tests/test_opt/test_coordiantes.py
@@ -898,8 +898,8 @@ def test_pic_generation_linear_angle_ref():
     assert PrimitiveImproperDihedral(3, 5, 2, 1) in pic
     assert sum(isinstance(ic, PrimitiveDihedralAngle) for ic in pic) == 1
     # check degrees of freedom = 3N - 6
-    _ = pic(m.coordinates.flatten())
-    assert np.linalg.matrix_rank(pic.B) == 3 * m.n_atoms - 6
+    x = m.coordinates.flatten()
+    assert np.linalg.matrix_rank(pic.get_B(x)) == 3 * m.n_atoms - 6
 
 
 def test_pic_generation_linear_angle_dummy():
@@ -915,8 +915,8 @@ def test_pic_generation_linear_angle_dummy():
     assert any(isinstance(ic, PrimitiveDummyLinearAngle) for ic in pic)
 
     # degrees of freedom = 3N - 5 for linear molecules
-    _ = pic(mol.coordinates.flatten())
-    assert np.linalg.matrix_rank(pic.B) == 3 * mol.n_atoms - 5
+    x = mol.coordinates.flatten()
+    assert np.linalg.matrix_rank(pic.get_B(x)) == 3 * mol.n_atoms - 5
 
 
 @work_in_tmp_dir()
@@ -958,8 +958,8 @@ def test_pic_generation_disjoint_graph():
     assert PrimitiveDistance(2, 3) not in pic
     assert PrimitiveBondAngle(1, 2, 3) not in pic
     # check degrees of freedom = 3N - 6
-    _ = pic(mol.coordinates.flatten())
-    assert np.linalg.matrix_rank(pic.B) == 3 * mol.n_atoms - 6
+    x = mol.coordinates.flatten()
+    assert np.linalg.matrix_rank(pic.get_B(x)) == 3 * mol.n_atoms - 6
 
     # if the bond between 2, 3 is made into a constraint, it will generate angles
     mol.constraints.distance = {(2, 3): mol.distance(2, 3)}
@@ -979,8 +979,8 @@ def test_pic_generation_chain_dihedrals():
     assert PrimitiveDihedralAngle(7, 4, 3, 6) in pic
 
     # check that the 3N-6 degrees of freedom are maintained
-    _ = pic(cumulene.coordinates.flatten())
-    assert np.linalg.matrix_rank(pic.B) == 3 * cumulene.n_atoms - 6
+    x = cumulene.coordinates.flatten()
+    assert np.linalg.matrix_rank(pic.get_B(x)) == 3 * cumulene.n_atoms - 6
 
 
 def test_pic_generation_square_planar():
@@ -998,5 +998,5 @@ def test_pic_generation_square_planar():
     # for sq planar, out-of-plane dihedrals are needed to have
     # all degrees of freedom
     pic = AnyPIC.from_species(ptcl4)
-    _ = pic(ptcl4.coordinates.flatten())
-    assert np.linalg.matrix_rank(pic.B) == 3 * ptcl4.n_atoms - 6
+    x = ptcl4.coordinates.flatten()
+    assert np.linalg.matrix_rank(pic.get_B(x)) == 3 * ptcl4.n_atoms - 6
diff --git a/tests/test_opt/test_crfo.py b/tests/test_opt/test_crfo.py
index a544a60..2d32f7f 100644
--- a/tests/test_opt/test_crfo.py
+++ b/tests/test_opt/test_crfo.py
@@ -235,7 +235,7 @@ def test_crfo_with_dihedral():
     constrained_distance = mol.distance(0, 1) + 0.1
     mol.constraints.distance = {(0, 1): constrained_distance}
 
-    CRFOptimiser.optimise(species=mol, method=XTB(), maxiter=15)
+    CRFOptimiser.optimise(species=mol, method=XTB(), maxiter=10)
 
     assert np.isclose(mol.distance(0, 1), constrained_distance, atol=1e-4)
 
diff --git a/tests/test_opt/test_qa.py b/tests/test_opt/test_qa.py
index 3831b8b..2afe12e 100644
--- a/tests/test_opt/test_qa.py
+++ b/tests/test_opt/test_qa.py
@@ -29,8 +29,7 @@ def test_trm_step():
     opt._step()
     step = np.array(opt._history.final) - np.array(opt._history.penultimate)
     step_size = np.linalg.norm(step)
-    # TODO: fix the DIC transform bug
-    # assert np.isclose(step_size, 0.1)
+    assert np.isclose(step_size, 0.1)
 
 
 @work_in_tmp_dir()