In this Letter we have presented a method for applying pressure on nanoparticles in the computer simulations, using an ideal gas as the pressure medium. Simulations have been performed under different isothermal conditions (200-400 K) and for pressures up to 60 GPa for different sizes of Ni nanoclusters (N = 336, 484, 736, 1004, 1956 Ni atoms). We have noticed that the surface energy depends on temperature, pressure, and cluster size and its dependence on the cluster size is significant. At constant temperature and pressure, surface energy decreases with cluster size. Also, at constant temperature and N, surface energy increases with pressure. (C) 2012 Elsevier B.V. All rights reserved.