"""Diffusion by an exchange process"""
from __future__ import print_function

from math import sqrt

from ase import Atoms, Atom
from ase.io import write
from ase.visualize import view
from ase.constraints import FixAtoms
from ase.optimize import QuasiNewton, MDMin
from ase.neb import NEB
from ase.calculators.emt import EMT

a = 4.0614
b = a / sqrt(2)
h = b / 2
initial = Atoms('Al2',
                positions=[(0, 0, 0),
                           (a / 2, b / 2, -h)],
                cell=(a, b, 2 * h),
                pbc=(1, 1, 0))
initial *= (2, 2, 2)
initial.append(Atom('Al', (a / 2, b / 2, 3 * h)))
initial.center(vacuum=4.0, axis=2)

final = initial.copy()
# move adatom to row atom 14
final.positions[-1, :] = initial.positions[14]
# Move row atom 14 to the next row
final.positions[14, :] = initial.positions[-1] + [a, b, 0]

view([initial, final])

# Construct a list of images:
images = [initial]
for i in range(5):
    images.append(initial.copy())
images.append(final)

# Make a mask of zeros and ones that select fixed atoms (the
# two bottom layers):
mask = initial.positions[:, 2] - min(initial.positions[:, 2]) < 1.5 * h
constraint = FixAtoms(mask=mask)
print(mask)

for image in images:
    # Let all images use an EMT calculator:
    image.set_calculator(EMT())
    image.set_constraint(constraint)

# Relax the initial and final states:
QuasiNewton(initial).run(fmax=0.05)
QuasiNewton(final).run(fmax=0.05)

# Create a Nudged Elastic Band:
neb = NEB(images)

# Make a starting guess for the minimum energy path (a straight line
# from the initial to the final state):
neb.interpolate()

# Relax the NEB path:
minimizer = MDMin(neb)
# minimizer = QuasiNewton(neb)
minimizer.run(fmax=0.05)

# Write the path to a trajectory:
view(images)
# 235 meV
write('jump3.traj', images)