Visualization Tutorial — Droplet Surface and Contact Angle

This tutorial demonstrates how to visualize a droplet and compute its contact angle using the wetting_angle_kit package. We’ll use the sliced contact angle method and visualize the resulting droplet with the DropletSlicedPlotter class.

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1. Overview

The visualization workflow involves the following steps:

1. Parse atomic positions from a trajectory file.

2. Identify water molecules (oxygen and hydrogen atoms).

3. Compute the droplet surface and contact angle using the sliced method.

4. Visualize the droplet, fitted circle, tangent, and wall.

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2. Import Required Modules

import numpy as np
from wetting_angle_kit.parser import (
    DumpParser,
    DumpWaterMoleculeFinder,
    DumpWallParser,
)
from wetting_angle_kit.contact_angle_method.sliced_method import ContactAngleSliced
from wetting_angle_kit.visualization_angles import DropletSlicedPlotter

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3. Define the Input Trajectory

filename = (
    "../wetting_angle_kit/tests/trajectories/traj_10_3_330w_nve_4k_reajust.lammpstrj"
)

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4. Identify Water Molecules

wat_find = DumpWaterMoleculeFinder(
    filename, particle_type_wall={3}, oxygen_type=1, hydrogen_type=2
)

oxygen_indices = wat_find.get_water_oxygen_ids(frame_index=0)
print("Number of water molecules detected:", len(oxygen_indices))

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5. Parse Atomic Coordinates

parser = DumpParser(filepath=filename)
oxygen_position = parser.parse(frame_index=10, indices=oxygen_indices)

coord_wall = DumpWallParser(filename, particule_liquid_type={1, 2})
wall_coords = coord_wall.parse(frame_index=1)

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6. Compute Contact Angles

processor = ContactAngleSliced(
    liquid_coordinates=oxygen_position,
    liquid_geom_center=np.mean(oxygen_position, axis=0),
    droplet_geometry="cylinder_y",
    delta_cylinder=5,
    max_dist=100,
    width_cylinder=21,
)

list_alfas, array_surfaces, array_popt = processor.predict_contact_angle()
print("Mean contact angles (°):", list_alfas)

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7. Visualize the Droplet

plotter = DropletSlicedPlotter(center=True, show_wall=True, molecule_view=True)

plotter.plot_surface_points(
    oxygen_position=oxygen_position,
    surface_data=array_surfaces,
    popt=array_popt[0],
    wall_coords=wall_coords,
    output_filename="droplet_plot.png",
    alpha=list_alfas[0],
)

print(" Plot saved as 'droplet_plot.png'")

Outputs