Allow modifying cutoff values from ASE calculator

Author: awvwgk

python/dftd3/ase.py

@@ -40,6 +40,7 @@
  method                   None         Method to calculate dispersion for
  damping                  None         Damping function to use
  params_tweaks            None         Optional dict with the damping parameters
+ realspace_cutoff         None         Optional dict to override cutoff values
  cache_api                True         Reuse generate API objects (recommended)
 ======================== ============ ============================================
 
@@ -63,6 +64,20 @@
 for damping parameters of a given method and prefers special two-body only
 damping parameters if available!
 
+The realspace cutoff parameters allow adjusting the distance values for which
+interactions are considered
+
+================== =========== ==========================================
+ Realspace cutoff   Default     Description
+================== =========== ==========================================
+ disp2              60 * Bohr   Pairwise dispersion interactions
+ disp3              40 * Bohr   Triple dispersion interactions
+ cn                 40 * Bohr   Coordination number counting
+================== =========== ==========================================
+
+Values provided in the dict are expected to be in Angstrom. When providing values
+in Bohr divide the inputs by the `ase.units.Bohr` constant.
+
 Example
 -------
 >>> from ase.build import molecule
@@ -144,6 +159,7 @@ class DFTD3(Calculator):
         "method": None,
         "damping": None,
         "params_tweaks": {},
+        "realspace_cutoff": {},
         "cache_api": True,
     }
 
@@ -235,8 +251,18 @@ def _create_api_calculator(self) -> DispersionModel:
                 _periodic,
             )
 
-        except RuntimeError:
-            raise InputError("Cannot construct dispersion model for dftd3")
+        except RuntimeError as e:
+            raise InputError("Cannot construct dispersion model for dftd3") from e
+
+        try:
+            if self.parameters.realspace_cutoff:
+                disp2 = self.parameters.realspace_cutoff.get("disp2", 60.0 * Bohr) / Bohr
+                disp3 = self.parameters.realspace_cutoff.get("disp3", 40.0 * Bohr ) / Bohr
+                cn = self.parameters.realspace_cutoff.get("cn", 40.0 * Bohr ) / Bohr
+
+                disp.set_realspace_cutoff(disp2=disp2, disp3=disp3, cn=cn)
+        except RuntimeError as e:
+            raise InputError("Cannot update realspace cutoff for dftd3") from e
 
         return disp
 
@@ -247,8 +273,8 @@ def _create_damping_param(self) -> DampingParam:
             params_tweaks = self.parameters.params_tweaks if self.parameters.params_tweaks else {"method": self.parameters.get("method")} 
             dpar = _damping_param[self.parameters.get("damping")](**params_tweaks)
 
-        except RuntimeError:
-            raise InputError("Cannot construct damping parameter for dftd3")
+        except RuntimeError as e:
+            raise InputError("Cannot construct damping parameter for dftd3") from e
 
         return dpar
 
@@ -273,8 +299,8 @@ def calculate(
 
         try:
             _res = self._disp.get_dispersion(param=_dpar, grad=True)
-        except RuntimeError:
-            raise CalculationFailed("dftd3 could not evaluate input")
+        except RuntimeError as e:
+            raise CalculationFailed("dftd3 could not evaluate input") from e
 
         # These properties are garanteed to exist for all implemented calculators
         self.results["energy"] = _res.get("energy") * Hartree