  We develop a novel method of replica-exchange molecular dynamics (REMD)
simulation, mass-scaling REMD (MSREMD) method, which improves trajectory
accuracy at high temperatures, and thereby contributes to numerical stability.
In addition, the MSREMD method can also simplify a replica-exchange routine by
eliminating velocity scaling. As a pilot system, a Lennard-Jones fluid is
simulated with the new method. The results show that the MSREMD method improves
the trajectory accuracy at high temperatures compared with the conventional
REMD method. We analytically demonstrate that the MSREMD simulations can
reproduce completely the same trajectories of the conventional REMD ones with
shorter time steps at high temperatures in case of the Nos\'e-Hoover
thermostats. Accordingly, we can easily compare the computational costs of the
REMD and MSREMD simulations. We conclude that the MSREMD method decreases the
instability and optimizes the computational resources with simpler algorithm
under the constant trajectory accuracy at all temperatures.
