Hi Oscar G:
Thanks for your reply.
As wrote in my first email, the sample is non-periodic in y-direction, i.e. BCs psp, so ‘iso’ cann’t be used here.
Slowing down the speed of heating a sample may be a way to reduce atoms fluctuation, but will dividing heating process into several steps cause some other side effects?
Steve, as you said ,‘any thermostat will have nearly the same fluctuations’, for a new lammps-user, can i understand your conclusion like this:
fluctuations are related to atoms position, atoms position are related to atoms velocity, finally atoms velocity are closely related to temperature.
So for a sample, no matter which thermosta i used, once it is heated to a same temperature, then fluctuations will be nearly same.
But as wrote in my first email, for a sample with initial dimensions, Lx=38.518729 Ly=139.40627 Lz=34.457144,
when heated to 1400k by “fix npt”, the dimensions are Lx=39.288336, Ly=145.97492, Lz= 35.221666;
when heated to 1400k by “fix nvt”, the dimensions are Lx=38.518729, Ly=153.85074, Lz= 34.457144;
As we can see, for “fix nvt”, Ly is lager than that of “fix npt”.
Though these results just show changes of dimensions, which can not be used to completely reflect fluctuations ,
i think fluctuations are related to changes of dimensions, the larger changes of dimensions are, the larger the atoms fluctuations will be.
All i want to is, my simulational results seem to show that for an non-periodic sample, different thermostat may cause different fluctuations.
If this kind of phenomenon does exist, then attention should be put on it.