randomxtc.py

import mdtraj as md
import numpy as np

n_frames = 100
coords = np.random.multivariate_normal(mean=[0, 0, 0], cov=[[2, 1, 0], [0, 1, 0], [0 ,0, 1]], size=n_frames)
coords = np.reshape(coords, (n_frames, 1, 3))

with md.XTCTrajectoryFile('output.xtc', 'w') as f:
    f.write(coords)