We had to calculate volume of obtained voids in the structure of copper GB highlighted by pink, blue and green

The shapes of voids are irregular.

ConvexHull() method from scipy.spatial

# Read the structure file
from siman.calc_manage import  smart_structure_read
st = smart_structure_read('path_to_POSCAR')

#create lists with atomic coordinates of corner atoms of our voids
pink = [73,83,87,104,107,113]
green = [97,104,105,106,107,108,113,206,207,208]
blue = [83,85,87,112,113,114]

for void, name in zip([pink,blue,green],['pink','blue','green']):
    pts_list=[]
    for at in void:
        pts_list.append(list(st.xcart[at]))

    #find the volume of space between points
    import scipy.spatial as ss
    import numpy as np
    hull = ss.ConvexHull(pts_list)
    print(f'Volume of {name} void: {hull.volume:.2f} A^3')

Volume of pink void: 8.73 A^3
Volume of blue void: 8.47 A^3
Volume of green void: 25.02 A^3