  We investigate the ergodicity and "hot solvent/cold solute" problems in
molecular dynamics simulations. While the kinetic moments and the stimulated
Nos\'e--Hoover methods improve the ergodicity of a harmonic-oscillator system,
both methods exhibit the "hot solvent/cold solute" problem in a binary liquid
system. These results show that the devices to improve the ergodicity do not
resolve the "hot solvent/cold solute" problem.
