Hi,
I’m trying to perform some basic tests of a reaxff force field, but am having a problem calculating the elastic modulus. When I run my script (below), it equilibrates fine, but running the deform I get;
Step CPULeft strain pxx (Gpa) pyy pzz Pressure Pot. Energy Temp
0 0 -1.4996035e-15 0.068125509 0.057837415 0.068388786 -639.36741 -202387.63 300.77279
1 2684.4725 2e-05 46.454471 41.715774 45.891651 -441029.35 -108863.53 201.8778
2 1438.653 4e-05 nan nan nan nan 2.4728187e-10 nan
…
This is likely the offending script lines, but I’ll attach the whole script;
fix 1 all npt temp 300.0 300.0 1000.0 y 0 0 1 z 0 0 1 drag 1.0
fix 2 all qeq/reax 1 0.0 10.0 1e-6 param.qeq
variable srate1 equal “1.0e10 / 1.0e15”
fix 3 all deform 1 x erate ${srate1} units box remap x
I have run the same script successfully using an EAM force field (NB: it was in metal units, so maybe I have made an error converting to real units?);
0 0 -3.72755e-16 0.051937011 0.042171079 0.053431467 -491.79852 -8163.7976 304.20259
1 56.313605 2e-05 0.047322721 0.040185164 0.050409926 -459.72603 -8163.8159 304.27358
2 52.113837 4e-05 0.047396477 0.04075393 0.050076485 -460.75631 -8163.8039 304.23182
…
500 44.975638 0.01 1.3595741 0.02241023 0.10438183 -4954.5539 -8160.2061 296.07452
As you can see, in the reaxff run, the temperature and pressure drop abruptly, but not in the EAM run. Perhaps I need to change the Tdamp/drag parameter or use a better thermostat?
Any help would be appreciated, kind regards,
Chris
Fe_bcc_tensile.in (4.48 KB)