Update src/nmreval/nmr/coupling.py

Change unit of dipolar distances to avoid problems with tolerances during minimization process.

src/nmreval/nmr/coupling.py

@@ -106,7 +106,7 @@ class HomoDipolar(Coupling):
 
     name = 'Homonuclear Dipolar'
     parameter = ['r']
-    unit = ['m']
+    unit = ['nm']
     choice = [
         (r'\gamma', 'nucleus', {k: k for k in gamma}),
         ('Spin', 'spin', OrderedDict([('1/2', 0.5), ('1', 1), ('3/2', 1.5), ('2', 2), ('5/2', 2.5), ('3', 3)])),
@@ -128,7 +128,7 @@ class HomoDipolar(Coupling):
             raise KeyError(f'Unknown nucleus {nucleus}')
 
         try:
-            coupling = mu0 / (4*pi) * hbar_joule * gamma_full[nucleus]**2 / (r+1e-34)**3
+            coupling = mu0 / (4*pi) * hbar_joule * gamma_full[nucleus]**2 / ((r*1e-9) + 1e-34)**3
         except ZeroDivisionError:
             return 1e318
 
@@ -143,7 +143,7 @@ class HeteroDipolar(Coupling):
 
     name = 'Heteronuclear Dipolar'
     parameter = ['r']
-    unit = ['m']
+    unit = ['nm']
     choice = [
         (r'\gamma_{1}', 'nucleus1', {k: k for k in gamma}),
         (r'\gamma_{2}', 'nucleus2', {k: k for k in gamma}),
@@ -172,7 +172,7 @@ class HeteroDipolar(Coupling):
             raise KeyError(f'Unknown nucleus {nucleus2}')
 
         try:
-            coupling = mu0 / (4*pi) * hbar_joule * gamma_full[nucleus1]*gamma_full[nucleus2] / r**3
+            coupling = mu0 / (4*pi) * hbar_joule * gamma_full[nucleus1]*gamma_full[nucleus2] / ((r+1e-9) + 1e34)**3
         except ZeroDivisionError:
             return 1e318