1"""Ideal gas calculator - the potential energy is always zero.""" 

2 

3import numpy as np 

4from ase.calculators.calculator import Calculator, all_changes 

5 

6 

7class IdealGas(Calculator): 

8 """The ideal gas: non-interacting atoms. 

9 

10 The ideal gas is atoms that do not interact. The potential is thus 

11 always zero, and so are forces and stresses (apart from the dynamic 

12 part of the stress, which is handled by the atoms themselves). 

13 

14 This calculator is probably only useful for testing purposes. 

15 """ 

16 

17 implemented_properties = ['energy', 'energies', 'forces', 

18 'stress', 'stresses'] 

19 

20 def calculate(self, atoms=None, properties=[], 

21 system_changes=all_changes): 

22 """'Calculate' the zero energies and their derivatives.""" 

23 super().calculate(atoms, properties, system_changes) 

24 n = len(self.atoms) 

25 self.results = { 

26 'energy': 0.0, 

27 'energies': np.zeros(n), 

28 'forces': np.zeros((n, 3)), 

29 'stress': np.zeros(6), 

30 'stresses': np.zeros((n, 6)), 

31 }