  We propose a new generalized-ensemble algorithm, which we refer to as the
multibaric-multithermal Monte Carlo method. The multibaric-multithermal Monte
Carlo simulations perform random walks widely both in volume space and in
potential energy space. From only one simulation run, one can calculate
isobaric-isothermal-ensemble averages at any pressure and any temperature. We
test the effectiveness of this algorithm by applying it to the Lennard-Jones
12-6 potential system with 500 particles. It is found that a single simulation
of the new method indeed gives accurate average quantities in
isobaric-isothermal ensemble for a wide range of pressure and temperature.
