Hi:
everyone,I’m a newbie here.
my script concerning command “fix npt” is listed below:
units metal
…
fix 1 all npt 3200.0 3200.0 0.1 xyz 1.0 1.0 0.1 drag 0.2
…
here comes the result.
Step Temp Volume Press Lx
0 3200 2653.9383 -74773.429 13.845127
we will notice the temperature is 3200 as we desired,however,the pressure is negative.so what does it mean.why it is
-74773.429 rather than 1.0 that I expect.
the initial temprature of the system can be setup via velocity command
what about initial pressure?I 'm puzzled.
I will appreciate all the kind help.thank you.
ChenJi
Material Science And Engineering Department
Xi’An Technological University
Xi’An,ShanXi Province,710032
P.R.C.
Hi:
everyone,I'm a newbie here.
my script concerning command "fix npt" is listed below:
units metal
....
fix 1 all npt 3200.0 3200.0 0.1 xyz 1.0 1.0 0.1 drag 0.2
....
here comes the result.
Step Temp Volume Press Lx
0 3200 2653.9383 -74773.429 13.845127
we will notice the temperature is 3200 as we desired,however,the pressure is negative.so what does it mean.why it is
-74773.429 rather than 1.0 that I expect.
the initial temprature of the system can be setup via velocity command.
what about initial pressure?I 'm puzzled.
why puzzled? at step 0 you get out what you put in.
the temperature is what you ask for because you initialize
the kinetic energy it to this value. the initial pressure
also depends on your initial positions and cell size, if
you chose them, so they have a negative pressure, that is
what you get... 
cheers,
axel.