Hi All,

I am trying to find the critical resolved shear stress in LAMMPS.For that, i am planning to apply shear through “”"“velocity”""" command WITHOUT RAMPING…(To Simulate Dislocation Motion). For beginning, i am first doing the same in a perfect crystal containing only 500 atoms( IF SHEAR IS APPLIED IN CORRECT WAY IN A PERFECT CRYSTAL WITH DEFAULT ORIENTATIONS, THEN I WILL PROCEED TO THE ORIGINAL PROBLEM). I am doing on Aluminium, a=4.05A and using Al_jnp.eam potential.I am dumping the shear force using fix store/force command…

But log file gives the force as ZERO in the upper region… I am not able to figure as to where am i making mistake. I am attaching the i/p file of Shear…

##################SHEAR########################

fix 10 boundary nve

fix 11 boundary temp/rescale 10 300.0 300.0 10 1.0

fix 12 mobile nvt temp 300.0 300.0 .01

fix 14 lower setforce 0.0 0.0 0.0

velocity upper set .00000018075 0 0 ###########Box height is 18.075A, so this gives strain = 1e-5 after running for 1000 steps.

fix 13 upper store/force

compute stress upper reduce sum f_13[1]

variable strain equal 1e-5

variable shearforce equal (c_stress/(lx*lz)) ######## Output from compute is in ev/A units, so this gives in ev/A^3 units…
variable shearstress equal (v_shear*160.2) ############ Stress in GPa

dump 1 all cfg 100 dump.* id type xs ys zs

thermo_style custom step temp pe v_strain v_shearstress

run 1000

minimize 1e-5 1e-5 10000 10000