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import numpy as np
from ase.build import bulk
from ase.calculators.lj import LennardJones
from ase.optimize.precon import Exp, PreconLBFGS
cu0 = bulk("Cu") * (2, 2, 2)
sigma = cu0.get_distance(0,1)*(2.**(-1./6))
lj = LennardJones(sigma=sigma)
# perturb the cell
cell = cu0.get_cell()
cell *= 0.95
cell[1,0] += 0.2
cell[2,1] += 0.5
cu0.set_cell(cell, scale_atoms=True)
energies = []
for use_armijo in [True, False]:
for a_min in [None, 1e-3]:
atoms = cu0.copy()
atoms.set_calculator(lj)
opt = PreconLBFGS(atoms, precon=Exp(A=3), use_armijo=use_armijo,
a_min=a_min, variable_cell=True)
opt.run(fmax=1e-3, smax=1e-4)
energies.append(atoms.get_potential_energy())
# check we get the expected energy for all methods
assert np.abs(np.array(energies) - -63.5032311942).max() < 1e-4
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