A new better comment on the save_extxyz subroutine

Author: mesonepigreco

Modules/Ensemble.py

@@ -822,7 +822,7 @@ def save_extxyz(self, filename, append_mode = True):
         for i, s in enumerate(self.structures):
             energy = self.energies[i] * Rydberg  # Ry -> eV
             forces = self.forces[i, :, :] * Rydberg  # Ry/A -> eV/A
-            stress = -self.stresses[i, :, :] * Rydberg /  Bohr**3 # Ry/Bohr^3 -> eV/A^3
+            stress = -self.stresses[i, :, :] * Rydberg /  Bohr**3 # Ry/Bohr^3 -> eV/A^3 (with ase conventions on sign)
             struct = s.get_ase_atoms()
 
             calculator = ase.calculators.singlepoint.SinglePointCalculator(struct, energy = energy,