# Set the calculation parameters
calc.set(prec='Accurate',
xc='PBE',
lreal=False,
nsw=30,
ediff=1e-8,
ibrion=2,
kpts=[3, 3, 3])
# Set the calculation mode first.
# Full structure optimization in this case.
# Not all calculators have this type of internal minimizer!
calc.set(isif=3)
print "Running initial optimization ... ",
print "Residual pressure: %.3f bar" % (cryst.get_isotropic_pressure(
cryst.get_stress()))
# Lets extract optimized lattice constant.
# MgO is cubic so a is a first diagonal element of lattice matrix
a = cryst.get_cell()[0, 0]
# Clean up the directory
calc.clean()
# Switch to cell shape+IDOF optimizer
calc.set(isif=4)
# Calculate few volumes and fit B-M EOS to the result
# Use +/-3% volume deformation and 5 data points
fit = cryst.get_BM_EOS(n=5, lo=0.97, hi=1.03)
calc.set(prec='Accurate',
xc='PBE',
lreal=False,
nsw=30,
ediff=1e-8,
ibrion=2,
kpts=[3, 3, 3])
# Set the calculation mode first.
# Full structure optimization in this case.
# Not all calculators have this type of internal minimizer!
calc.set(isif=3)
print("Running initial optimization ... ", end=' ')
print("Residual pressure: %.3f bar" %
(cryst.get_isotropic_pressure(cryst.get_stress())))
# Clean up the directory
calc.clean()
# Switch to cell IDOF optimizer
calc.set(isif=2)
# Elastic tensor by internal routine
Cij, Bij = cryst.get_elastic_tensor(n=5, d=0.2)
print("Cij (GPa):", Cij / units.GPa)
# Now let us do it (only c11 and c12) by hand
# with 3rd order polynomial fitting the points.
sys = []
for d in linspace(-0.2, 0.2, 10):
calc.set(prec = 'Accurate',
xc = 'PBE',
lreal = False,
nsw=30,
ediff=1e-8,
ibrion=2,
kpts=[3,3,3])
# Set the calculation mode first.
# Full structure optimization in this case.
# Not all calculators have this type of internal minimizer!
calc.set(isif=3)
print "Running initial optimization ... ",
print "Residual pressure: %.3f bar" % (
cryst.get_isotropic_pressure(cryst.get_stress()))
# Clean up the directory
calc.clean()
# Switch to cell IDOF optimizer
calc.set(isif=2)
# Elastic tensor by internal routine
Cij, Bij=cryst.get_elastic_tensor(n=5,d=0.2)
print "Cij (GPa):", Cij/units.GPa
# Now let us do it (only c11 and c12) by hand
# with 3rd order polynomial fitting the points.
sys=[]
