Hi, Let me insist in this question, as I have had no answer yet. > > 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? > Later I saw in the CP source that there is a subroutine 'add_thermal_stress', (which seems better than just 'add_thermal_press'),
cpr_mod.f90: subroutine add_thermal_stress( stress, pmass, omega, h, vels, nsp, na ) However, I found no CALL to this subroutine. Then my doubt increased. Eduardo
