[lammps-users] Help on four LAMMPS Questions!

I got four questions when using LAMMPS.

Question 1: How to formulate an ensemble consisted of two types of
atoms (i.e., CU and AL) in LAMMPS input script?

Question 2: A stretched nanowire should always have positive ensemble
stress. However, when using thermo-pressure (output in pressure.cpp)
to measure the ensemble, I sometimes observe the negative stress. Why
did it happen?

Question 3: What is the thermo-pressure unit of LAMMPS when used to
simulate metal?

Question 4: How to define an sphere indenter (in 3D cases)?
The script command
"fix 4 all indent 10.0 sphere 10.0 10.0 20.0 2.5 vel 0.0 0.0 -1.0"
always leads to following error message
"ERROR: Illegal fix indent command".

Thanks for your attention!

Hugh

Question 1: How to formulate an ensemble consisted of two types of
atoms (i.e., CU and AL) in LAMMPS input script?

The data file you read specifies the type of each atom. Give each atom
a 1 or 2 and its up to you to set their mass, pair-potential parameters
to make them Cu vs Al.

Question 2: A stretched nanowire should always have positive ensemble
stress. However, when using thermo-pressure (output in pressure.cpp)
to measure the ensemble, I sometimes observe the negative stress. Why
did it happen?

I don’t know. Possibly your boundary conditions, or non-periodicity might
affect the stress/pressure value being computed. Also, pressure values
oscillate a lot.

Question 3: What is the thermo-pressure unit of LAMMPS when used to
simulate metal?

bars - see the doc page on the units command

Question 4: How to define an sphere indenter (in 3D cases)?
The script command
“fix 4 all indent 10.0 sphere 10.0 10.0 20.0 2.5 vel 0.0 0.0 -1.0”
always leads to following error message
“ERROR: Illegal fix indent command”.

this command works fine in my LAMMPS - are you sure you have an up-to-date
patched version? The fix indent command did have a syntax change a while
back.

Steve