[lammps-users] Question about fix box/relax

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1

Dear users:

Could someone help me understand what is happening in the fix box/relax command? I understand that it is creating a new objective function: E=U+Pt(V-V0)+E_strain. In my simulation I am setting the desired pressure to 0. Thus, I’m particularly interested in how E_strain is calculated. I’ve looked at the paper by Parrinello and Rahman which describes strain as a function of the original lattice vectors and the updated lattice vectors. How does one get the updated lattice vectors?

Thanks,

Shawn Coleman
University of Arkansas

2

Aidan is the best person to do this.

Steve

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Not lattice vectors of the crystal, but periodic box dimensions which can be
printed out in the thermo output using the keywords lx, ly, lz, xy, xz, yz.
The strain energy calculates a difference between the current value of these
box dimensions and those of the reference box (see nreset keyword for info
on how to update the reference box at regular intervals).

Aidan