Question about strain rates in fix nvt/uef

Hi all,

I am reading the documentation for the fix nvt/uef method and found some inconsistencies in the documentation.

https://docs.lammps.org/fix_nh_uef.html

First, in the third paragraph of the description, there mentions the keyword eps but it is not shown in the syntax. I think it should be erate instead.

Second, the command requires to provide engineering strain rate edot_x and edot_y for x and y directions, and the strain rate for z direction is computed by -(edot_x+edot_y). However, if edots are engineering strain rates, this relationship between strain rates does not give a conserved volume. If edots are true strain rates, then the volume is conserved. I wonder if this fix is controlling the true strain rates or I misunderstood something.

Thank you for any idea or help.

Hi @Danyang_Chen

Indeed you have found a typo- thanks for pointing that out. I don’t know the current mechanism to correct it, but I will do so when I get a chance (unless you would like to do so first :slight_smile: ).

The strain rates are indeed true strain rates.

1 Like

That’s the awesome thing about open source – you can submit a pull request to the LAMMPS repo, just like with any code bug. The relevant source file is here: https://github.com/lammps/lammps/blob/c092de9bc39de0600702168d1aa025582bba1d2c/doc/src/fix_nh_uef.rst

It is already included in a pending pull request :smile: