Entropy and atomic collisions Suppose there is a beam of atoms moving with constant velocity in empty space. There are no collisions between the atoms. The temperature  is essentially zero since velocities of atoms are all equal to the velocity of the center of mass.
Now let’s trap the atomic beam into a box. When atoms collide with walls, kinetic energy of the center of mass will be lost, and will turn into temperature. In addition, entropy of the system will increase. 
Does this mean that entropy is growing due to collisions of atoms with the walls? So essentially collision events drive entropy growth?
What is it about the collisions that makes them increase entropy, is it due to quantum randomness of outcomes?
 A: When you have a distribution of particles in a single energy state and compare that to a distribution with particles arranged in multiple energy states the entropy values will be significantly different. You can work that out for a even if you do not view it from the perspective of microstates and instead view the system by understanding it from the perspective of second law of thermodynamics you would see an increase in entropy. This perspective is seen in your question itself when you say "kinetic energy of the center of mass will be lost, and will turn into temperature." What you do mean to say is that the kinetic energy will turn into heat.
To sum up the answer collision events should tend to increase the entropy to the theoretical maximum unless there is some catch in the problem.
A: The first frame of reference is moving with the gas particles. The gas particles have ZERO velocity in their frame.
The next step is to "put them in a box" and have them "collide with the walls". The step does work on the particles. It causes them to move from one reference frame to another. The work that is done is the integration of the force over distance that is required to change their velocity to the new reference frame. That work is expressed as a change in kinetic energy to internal energy. Since the gas particles were originally moving as referenced in the new frame, their kinetic energy decreases to move them to the new reference frame. We stop them or slow them down. According to energy conservation, the internal energy of the gas particles must therefore increase. An increase in internal energy causes the gas temperature to increase.
So, as we move gas particles in their initial reference frame where they are not moving (but where their reference frame IS moving) to a new reference frame that is static so as to have them collide with (static) walls, the internal energy of the gas particles increases. The temperature increases. The entropy distribution changes. Entropy increases.
We cannot melt ice just by moving it fast enough. But we can melt it by moving it fast enough and having it hit against a static wall adiabatically.
