The discussion revolves around the calculation of the center of mass in molecular dynamics (MD) simulations, specifically addressing the computational method of subtracting the average velocity from each atom's velocity to achieve a zero velocity for the center of mass. Participants explore the relationship between mass-weighted average velocity and the velocity of the center of mass.
Participants express differing views on the equivalence of mass-weighted average velocity and center of mass velocity, indicating that the discussion remains unresolved with multiple competing interpretations.
There are potential limitations in the assumptions made regarding the definitions of average velocity and center of mass, as well as the mathematical steps involved in the calculations, which remain unresolved.
Can you see that the [mass-weighted] average velocity is equal to the velocity of the center of mass?xperrylinn said:When calculating the center of mass for an MD simulation, I've seen a few codes that subtract the average velocity from each atoms velocity. I think the reasoning behind this is that you want the velocity of center of mass for the simulation to be zero, which I understand, but I don't understand computationally how subtracting the average velocity from each velocity achieves this.
The correct way to compute a weighted average is to divide by the sum of the weights, not the count of items.xperrylinn said:mass-weighted average velocity = (sum each atom's momentum) / (num atoms)