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# creates: lattice_constant.csv
import numpy as np
from ase.build import bulk
from ase.calculators.emt import EMT
from ase.io import Trajectory, read
a0 = 3.52 / np.sqrt(2)
c0 = np.sqrt(8 / 3.0) * a0
# --- literalinclude division line 1 ---
traj = Trajectory('Ni.traj', 'w')
# --- literalinclude division line 2 ---
eps = 0.01
for a in a0 * np.linspace(1 - eps, 1 + eps, 3):
for c in c0 * np.linspace(1 - eps, 1 + eps, 3):
ni = bulk('Ni', 'hcp', a=a, c=c)
ni.calc = EMT()
ni.get_potential_energy()
traj.write(ni)
# --- literalinclude division line 3 ---
configs = read('Ni.traj@:')
energies = [config.get_potential_energy() for config in configs]
a = np.array([config.cell[0, 0] for config in configs])
c = np.array([config.cell[2, 2] for config in configs])
# --- literalinclude division line 4 ---
functions = np.array([a**0, a, c, a**2, a * c, c**2])
p = np.linalg.lstsq(functions.T, energies, rcond=-1)[0]
# --- literalinclude division line 5 ---
p0 = p[0]
p1 = p[1:3]
p2 = np.array([(2 * p[3], p[4]), (p[4], 2 * p[5])])
a0, c0 = np.linalg.solve(p2.T, -p1)
with open('lattice_constant.csv', 'w') as fd:
fd.write(f'{a0:.3f}, {c0:.3f}\n')
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