Dear LAMMPS users,

I want to calculate the stress auto-correlation function for my system and have two questions regarding to LAMMPS.

- I have the error as ‘Fix ave/correlate compute does not calculate a vector’ reported and my scripts are:

compute 1 all stress/atom NULL

fix 3 all ave/correlate 1 10 1000 c_1[4] c_1[5] c_1[6] file aout.correlate

I would like to have the stress of xy, xz, yz correlate to themselves. Could you kindly point out what’s wrong in the script?

- what if I would like to calculate ave/correlate of pxy,pxz,pyz from thermo_style? Can I simply replace c_1[4] c_1[5] c_1[6] with pxy pxz pyz? Or should I store pxy, pxz and pyz first, then take them as variables?

Many thanks,

Sunnia

Dear LAMMPS users,

I want to calculate the stress auto-correlation function for my system and

have two questions regarding to LAMMPS.

1) I have the error as 'Fix ave/correlate compute does not calculate a

vector' reported and my scripts are:

compute 1 all stress/atom NULL

fix 3 all ave/correlate 1 10 1000 c_1[4] c_1[5] c_1[6] file

aout.correlate

I would like to have the stress of xy, xz, yz correlate to themselves.

Could you kindly point out what's wrong in the script?

compute stress/atom does not compute a global property, but a per-atom

one. so the error message is correct.

2) what if I would like to calculate ave/correlate of pxy,pxz,pyz from

thermo_style? Can I simply replace c_1[4] c_1[5] c_1[6] with pxy pxz pyz?

no, please see the fix ave/correlated documentation.

Or should I store pxy, pxz and pyz first, then take them as variables?

how about defining an instance of compute pressure?

axel.

Dear axel.

Is this a right way to compute the pressure (or say, stress)? See below:

compute 1 all stress/atom NULL

compute 2 all reduce sum c_1[4] c_1[5] c_1[6]

variable pxy equal -c_2[1]/(3*vol)

variable pxz equal -c_2[2]/(3*vol)

variable pyz equal -c_2[3]/(3*vol)

And then compute the stress auto-correlation function in the way as:

fix 3 all ave/correlate 1 10 1000 pxy pxz pyz file auto.correlate

If this will give me what I want?

Best wishes,

Sunnia

thank you very much for your commends.

Best wishes,

Sunnia