  An efficient approach of measuring the absolute free energy in parallel
tempering Monte Carlo using the exponential averaging method is discussed and
the results are compared with those of population annealing Monte Carlo using
the three-dimensional Edwards-Anderson Ising spin glass model as benchmark
tests. Numerical results show that parallel tempering, even though uses a much
less number of temperatures than population annealing, can nevertheless equally
efficiently measure the absolute free energy by simulating each temperature for
longer times.
