  In this work, we report a new method to simulate active Brownian particles
(ABPs) in molecular dynamics (MD) simulations. Immersed in a fluid, each ABP
consists of a head particle and a spherical phantom region of fluid where the
flagellum of a microswimmer takes effect. The orientation of the active
particle is governed by a stochastic dynamics, with the orientational
persistence time determined by the rotational diffusivity. To hydrodynamically
drive the active particle as a pusher, a pair of active forces are exerted on
the head particle and the phantom fluid region respectively. The active
velocity measured along the particle orientation is proportional to the
magnitude of the active force. The effective diffusion coefficient of the
active particle is first measured in free space, showing semi-quantitative
agreement with the analytical result predicted by a minimal model for ABPs. We
then turn to the probability distribution of the active particle in confinement
potential. We find that the stationary particle distribution undergoes an
evolution from the Boltzmann-type to non-Boltzmann distribution as the
orientational persistence time is increased relative to the relaxation time in
the potential well. From the stationary distribution in confinement potential,
the active part of the diffusion coefficient is measured and compared to that
obtained in free space, showing a good semi-quantitative agreement while the
orientational persistence time varies greatly relative to the relaxation time.
