[lammps-users] how to calculate shear stress, and get shear stress-strain relation?

Dear all,

I used command :
fix 1 all nvt 1200 1200 0.1
fix 2 all deform 1 xy erate 0.0001 remap v units box
to do the shear transformation

and used:

thermo_style pxy

to output the shear pressure tensor in every 1000 steps, looks like the following data:
step Temp PotEng TotEng Press Pxy Pyz Pxz
8500000 1173.7818 -21251.971 -20645.23 -292.91765 958.70412 -1167.5353 -295.14245
8501000 1204.5979 -21262.333 -20639.663 -14.527777 -378.7411 -500.71024 -608.63673
8502000 1189.5524 -21277.387 -20662.494 -752.79207 1119.441 -606.30654 -65.883594
8503000 1221.7777 -21274.894 -20643.344 -1089.3421 428.60665 1417.0084 607.68505
8504000 1212.3456 -21293.602 -20666.926 -1883.1043 1206.7776 268.1898 -403.13787
8505000 1184.321 -21287.096 -20674.907 -1234.8631 238.91603 792.41293 1262.584
8506000 1188.1363 -21276.228 -20662.067 -1181.7765 447.10585 -75.708588 -182.75491
8507000 1160.3746 -21267.069 -20667.258 -574.67166 169.86158 -73.845599 280.43115
8508000 1213.0483 -21285.104 -20658.066 -1384.7824 226.90259 947.44552 605.73889
8509000 1202.7442 -21272.252 -20650.54 -511.10659 -1110.847 -611.18248 55.277843
8510000 1207.0475 -21280.211 -20656.275 -1941.1877 488.96585 -776.02866 652.01971

but the pxy are oscillated around 0, I want to know how can I get the shear stress from this data? time averange? and plot the shear stress-strain?
Thank very much!!

best regards,

Guan Pengfei,

Pressures fluctuate, so how do you know this is wrong? The
kinetic component probably needs to have the shear removed,
which you can do with compute temp/deform. The NVT
fix can also mess up the dynamics when applied to a changing
box, so you probably want to monitor that carefully.

Steve