The above equation may be rewritten as M X ¨ ¨ ⏟ ⏟ inertial force + ∇ ∇ U ( X ) ⏟ ⏟ potential force + ζ ζ X ˙ ˙ ⏟ ⏟ viscous force − − 2 ζ ζ k B T R ( t ) ⏟ ⏟ random force = 0 In Brownian dynamics, the inertial force term M X ¨ ¨ ( t ) is so much smaller than the other three that it is considered negligible. In this case, the equation is approximately