import numpy as np

size = 9
percentage_max = 0.08
xis = np.linspace(0.1 * (1-percentage_max), 0.1 * (1+percentage_max), size)

E_n = [
 85219342462.9973,
 85219254693.4412,
 85219173007.4296,
 85219096895.7433,
 85219025899.6604,
 85218959605.1170,
 85218897637.6421,
 85218839657.9502,
 85218785358.0968
]

percentage = np.empty(size)

for i in range(len(xis)):
    percentage[i] = (E_n[i] - E_n[size//2])/E_n[size//2]*100

print(percentage)

# [ 3.71470260e-04  2.68477348e-04  1.72623153e-04  8.33101319e-05
#   0.00000000e+00 -7.77931251e-05 -1.50508665e-04 -2.18544754e-04
#  -2.82262747e-04]
[((5, 6, 5, 75), 'numpy.linspace', 'np.linspace', ({(5, 18, 5, 42): '0.1 * (1 - percentage_max)', (5, 44, 5, 68): '0.1 * (1 + percentage_max)', (5, 70, 5, 74): 'size'}, {}), '(0.1 * (1 - percentage_max), 0.1 * (1 + percentage_max), size)', True, 'import numpy as np\n'), ((19, 13, 19, 27), 'numpy.empty', 'np.empty', ({(19, 22, 19, 26): 'size'}, {}), '(size)', True, 'import numpy as np\n')]