Image of a general periodic box with two atoms in the unit cell

2D_periodic_box.py

import matplotlib.pyplot as plt
from itertools import product 
import numpy as np

a,b = np.array([4,1]),np.array([1,3])

fig,ax = plt.subplots(1,1,figsize=(5,5))
ax.set_xlim(-6,8)
ax.set_ylim(-6,8)
ax.set_axis_off()
ax.axhline(0,color='k')
ax.axvline(0,color='k')
ax.arrow(0, 0, 4, 1, head_width=0.3, head_length=0.1, width=0.1, fc='r', ec='r',alpha=1,zorder=2)
ax.arrow(0, 0, 1, 3, head_width=0.3, head_length=0.1, width=0.1, fc='g', ec='g',alpha=1,zorder=2)

ax.plot([1, 5], [3, 4], '-b',lw=2)
ax.plot([4, 5], [1, 4], '-b',lw=2)

for f in range(-5,6):
    x,y = f*b
    al = 12
    bl = al/4
    ax.plot([-al+x,al+x],[-bl+y,bl+y],'--k',lw=1)
    
for f in range(-5,6):
    x,y = f*a
    al = 12
    bl = 3*al
    ax.plot([-al+x,al+x],[-bl+y,bl+y],'--k',lw=1)

p1 = np.array([0.7,1])
p2 = np.array([4.1,3])

for c,d in product(range(-2,3),repeat=2):
    ax.scatter(*(p1+c*a+d*b),marker='o',color='k')
    ax.scatter(*(p2+c*a+d*b),marker='x',color='k')

plt.tight_layout()
plt.savefig('pbc.pdf', dpi=100, transparent=True)    
plt.show(fig)