Abstract
Pressure in molecular dynamics system is obtained through forces acted on molecules in a region defining pressure by molecules outside of it However, in a very small system such asrequiredin nano scale technology, especially at fluid phase, many particles move across the boundary of the region. Therefore it is important how we should take averages with respect to time and volume to obtain the pressure. In this paper, three types of definition of pressure are calculated. As a result the relation between pressure and the system volume (the number of particles) is clarified in such a nano scale sm all system.
