Hello,users:
I feel it difficult to understand the characteristics of “a simulation box” in LAMMPS.
I define my simulation box by “read_data” command and the data file comes from the transformation of a CIF file by OVITO software.
Here is the sentences controlling the size of the simulation box in the data file produced by OVITO:
0.0 10.5 xlo xhi
0.0 10.5 ylo yhi
0.0 10.5 zlo zhi
In fact, since this data file comes from a CIF file which contains the information of lattice parameters(a,b,c), the size of simulation box in this data file should perfectly equal the three lattice parameters. But what will happen if i manually change these numbers(e.g. 10.5 becomes 11, 21 or 31.5)
LAMMPS will see the extra volumes produced by this way as vacuum?
I want to study the hydrogen diffusion in the inner of ZrO2 solid.
If so, when I manually rewrite these numbers and make them bigger, will the ZrO2 suprcell no longer consistent when considering the periodic boundary conditions?
Besides, I concern the lattice parameters more than the size of simulation box because I want to calculate thermal expansion coefficient.
But it seems LAMMPS can not directly get the lattice parameters of a crystal.
Is it OK? if I just calculate the lattice parameters from the size of simulation box by a simple division:
that is to say, if the simulation box perfectly contains three ZrO2 unit cell along the x direction of the simulation box. Then the lattice parameters ‘a’ of the ZrO2 unit cell is perfectly equal lx/3 (lx is the size of simulation box along its x direction)
The final problem.
I have noticed the size of simulation box dynamically changed with a NPT thermostat. But why they always have Isotropic variation
key sentences in my ‘in file’ :
fix ensemble2 all npt temp 900 900 10 iso 0 0 100
I guess it is caused by " iso "?
If I want to simulation the anisotropy change of lattice parameters of ZrO2 unit cell, “fix npt temp aniso” is necessary and OK ?
Any advice and instruction will be welcome and appreciated.
Baoshuai