from ase import Atom, Atoms

m = Atoms('H2')
a = m[0]
b = Atom('H')
for c in [a, b]:
    assert c.x == 0
    c.z = 24.0
    assert c.position[2] == 24.0
    assert c.symbol == 'H'
    c.number = 92
    assert c.symbol == 'U'
    c.symbol = 'Fe'
    assert c.number == 26
    c.tag = 42
    assert c.tag == 42
    c.momentum = (1,2,3)
assert m[0].tag == 42
momenta = m.get_momenta()
m = Atoms('LiH')
for a in m:
    print a.symbol
for a in m:  
    if a.symbol == 'H':
        a.z = 0.75
assert m.get_distance(0, 1) == 0.75
a = m.pop()
m += a
del m[:1]
print m