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"""Demonstrates molecular dynamics with constant energy."""
from ase import units
from ase.lattice.cubic import FaceCenteredCubic
from ase.md.velocitydistribution import MaxwellBoltzmannDistribution
from ase.md.verlet import VelocityVerlet
# Use Asap for a huge performance increase if it is installed
use_asap = True
if use_asap:
from asap3 import EMT
size = 10
else:
from ase.calculators.emt import EMT
size = 3
# Set up a crystal
atoms = FaceCenteredCubic(
directions=[[1, 0, 0], [0, 1, 0], [0, 0, 1]],
symbol='Cu',
size=(size, size, size),
pbc=True,
)
# Describe the interatomic interactions with the Effective Medium Theory
atoms.calc = EMT()
# Set the momenta corresponding to T=300K
MaxwellBoltzmannDistribution(atoms, temperature_K=300)
# We want to run MD with constant energy using the VelocityVerlet algorithm.
dyn = VelocityVerlet(atoms, 5 * units.fs) # 5 fs time step.
def printenergy(a=atoms): # store a reference to atoms in the definition.
"""Function to print the potential, kinetic and total energy."""
epot = a.get_potential_energy() / len(a)
ekin = a.get_kinetic_energy() / len(a)
print(
'Energy per atom: Epot = %.3feV Ekin = %.3feV (T=%3.0fK) '
'Etot = %.3feV' % (epot, ekin, ekin / (1.5 * units.kB), epot + ekin)
)
# Now run the dynamics
dyn.attach(printenergy, interval=10)
printenergy()
dyn.run(200)
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