# Interoperability with Atomic Simulation Environment¶

• quippy Potential objects can be used as ASE calculators, and vice-versa
• quippy Atoms object is interoperable with ASE Atoms
• Can use standard ASE tools, plus communicate with other packages using ASE as lingua franca

## Example: vacancy formation energy¶

• Generate structure with ASE lattice tools
• Stillinger-Weber potential implementation from QUIP
• Elastic constant fitting routine from matscipy, internal relaxations with ASE FIRE minimiser
[1]:

%pylab inline
from ase.build import bulk
from ase.optimize import FIRE
from quippy.potential import Potential
from quippy.potential import Minim

si = bulk('Si', a=5.44, cubic=True)
sw_pot = Potential('IP SW') # call into Fortran code
si.set_calculator(sw_pot)
e_bulk_per_atom = si.get_potential_energy()/len(si)

# call general purpose elastic constants calculator
#   using ASE Atoms and QUIP Potential
from matscipy.elasticity import fit_elastic_constants
Cij = fit_elastic_constants(si, optimizer=FIRE,
symmetry='cubic', logfile='-')
vac1 = si.copy()
vac1 *= (3, 3, 3)
half_cell = np.diag(vac1.cell)/2.
vac_atom = ((vac1.positions - half_cell)**2).sum(axis=1).argmin()
del vac1[vac_atom]

vac1.set_calculator(sw_pot)
vac1.rattle(0.01)
opt = Minim(vac1, method='cg_n') # big cell, use Fortran minimiser
opt.run(fmax=1e-6)
e_vac = vac1.get_potential_energy() - e_bulk_per_atom*len(vac1)
print 'SW vacancy formation energy', e_vac, 'eV'

Populating the interactive namespace from numpy and matplotlib
Step     Time          Energy         fmax
FIRE:    0 16:22:44      -34.635777        0.3247
FIRE:    1 16:22:44      -34.642625        0.2026
FIRE:    2 16:22:44      -34.646995        0.0046
Step     Time          Energy         fmax
FIRE:    0 16:22:44      -34.670667        0.1584
FIRE:    1 16:22:44      -34.672303        0.0999
FIRE:    2 16:22:44      -34.673382        0.0046
Step     Time          Energy         fmax
FIRE:    0 16:22:44      -34.678737        0.0000
Step     Time          Energy         fmax
FIRE:    0 16:22:44      -34.660845        0.1508
FIRE:    1 16:22:44      -34.662341        0.0972
FIRE:    2 16:22:44      -34.663394        0.0090
Step     Time          Energy         fmax
FIRE:    0 16:22:44      -34.617822        0.2945
FIRE:    1 16:22:44      -34.623549        0.1917
FIRE:    2 16:22:44      -34.627707        0.0221

WARNING:quippy.potential:Minim atoms is not quippy.Atoms instance, copy forced!

Fitting C_11
Strain array([-0.02, -0.01,  0.  ,  0.01,  0.02])
Stress array([-2.56097717, -1.01273495,  0.5027424 ,  1.98320536,  3.42678422]) GPa
Cij (gradient) / GPa    :     149.714630969
Error in Cij / GPa      :     1.19249995513
Correlation coefficient :     0.999904848087
Setting C11 (1) to 0.934445 +/- 0.007443

Fitting C_21
Strain array([-0.02, -0.01,  0.  ,  0.01,  0.02])
Stress array([-1.0766539 , -0.26645127,  0.5027424 ,  1.23340389,  1.92788225]) GPa
Cij (gradient) / GPa    :     75.0892745799
Error in Cij / GPa      :     1.31766559061
Correlation coefficient :     0.999538422023
Setting C21 (7) to 0.468670 +/- 0.008224

Fitting C_31
Strain array([-0.02, -0.01,  0.  ,  0.01,  0.02])
Stress array([-1.0766539 , -0.26645127,  0.5027424 ,  1.23340389,  1.92788225]) GPa
Cij (gradient) / GPa    :     75.0892745799
Error in Cij / GPa      :     1.31766559061
Correlation coefficient :     0.999538422023
Updating C31 (7) with value 0.468670 +/- 0.008224

Fitting C_44
Strain array([-0.02, -0.01,  0.  ,  0.01,  0.02])
Stress array([ -1.15145968e+00,  -5.81643079e-01,  -9.46417971e-15,
5.90131462e-01,   1.18570415e+00]) GPa
Cij (gradient) / GPa    :     58.4610219649
Error in Cij / GPa      :     0.295085346333
Correlation coefficient :     0.999961785442
Setting C44 (4) to 0.364885 +/- 0.001842

[[ C11  C12  C12               ]
[ C12  C11  C12               ]
[ C12  C12  C11               ]
[                C44          ]
[                     C44     ]
[                          C44]]

=

[[ 149.71   75.09   75.09    0.      0.      0.  ]
[  75.09  149.71   75.09    0.      0.      0.  ]
[  75.09   75.09  149.71    0.      0.      0.  ]
[   0.      0.      0.     58.46    0.      0.  ]
[   0.      0.      0.      0.     58.46    0.  ]
[   0.      0.      0.      0.      0.     58.46]]
C_11 = 149.71 +/- 1.19 GPa
C_12 = 75.09 +/- 1.32 GPa
C_44 = 58.46 +/- 0.30 GPa
SW vacancy formation energy 4.30106655261 eV

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