Hi everybody, I have a doubt concernig the pressure reported by pw or cp in a molecular dynamics run. The stress tensor and its trace (the pressure) reported in molecular dynamics by pwscf and other quantum codes is a static pressure. In a molecular dinamics simulation, if I want the "real" pressure, I must add dp=(N/V) k_B T, N being the number of atoms and V the volume of the cell, and T the instantaneous temperature or its meand value.
In other words, the pressure of a non ideal gas (or liquid) is P=(N/V) k_B T + virial term (do not worry about the exact expression), then I understand that the pressure given by the codes is equivalent to the virial term. Is this correct? I found strange that nobody mentions it. Therefore, I understand that to have the "real" pressure I must add (N/V)k_B T to the pressure reported by pw or cp. Please, correct me if I am wrong. Next level of question. If I do Parrinello-Rahman dynamics with a Nose thermostast, what is the pressure specified by the keyword press ? Does it include the thermal pressure? I see that there is also a Nose thermostast for the cell. What is its importance? Is it neccessary to use this cell thermostat for the NPT ensemble? Thanks Eduardo
