The Hold atoms animation holds atoms positions fixed between two frames.
See also animations: Move atoms
First, select a group of particles that you want to have fixed positions between two frames.
Then, double-click on the Hold atoms animation effect in the Animation panel of the Animator or click Animation menu > Motion > Hold atoms.
The selected group of particles will be held at the fixed positions between the two keyframes. Move the keyframes of the animation as needed.
Note: You can always move the keyframes of the animation.
Some examples of presentations available on SAMSON Connect - Documents that use this animation: