Improve readability of ASE calculator code

python/metatensor-torch/metatensor/torch/atomistic/ase_calculator.py

@@ -349,16 +349,16 @@ def calculate(
 
  if do_backward:
  with record_function("ASECalculator::run_backward"):
- energy.backward(-torch.ones_like(energy))
+ energy.backward()
 
  with record_function("ASECalculator::convert_outputs"):
  if "forces" in properties:
- forces_values = system.positions.grad.reshape(-1, 3)
+ forces_values = -system.positions.grad.reshape(-1, 3)
  forces_values = forces_values.to(device="cpu").to(dtype=torch.float64)
  self.results["forces"] = forces_values.numpy()
 
  if "stress" in properties:
- stress_values = -strain.grad.reshape(3, 3) / atoms.cell.volume
+ stress_values = strain.grad.reshape(3, 3) / atoms.cell.volume
  stress_values = stress_values.to(device="cpu").to(dtype=torch.float64)
  self.results["stress"] = _full_3x3_to_voigt_6_stress(
  stress_values.numpy()