[lammps-users] Relaxing a Substrate for Indentation

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1

Hi everybody,

As I’m working with this relaxation issue now for over two month with little success, I have to ask specifically in the mailinglist: Has anybody experiences with relaxing a substrate with lateral periodic boundary conditions, bottom fixed, top open in an fcc structure with a boxlength of ~250Angstrom? By relaxation I mean T=0 and p=0. Potential could be any of LJ, Morse or EAM. A procedure or even better a working script would be very nice to see :slight_smile:

This is a short summary of what I tried so far:
The minimizator (cg/sd) results in oscillations in the surface. So I’m using MD directly; temp/rescale can achieve T=0 and pressure relaxation is applied in the lateral direction to p_ij=0. This method works nicely for small systems (boxlength ~100Angstroms). But for the bigger systems it takes a too long cpu-time to relax the substrate. Without a achieving a milestone in required simulation time I varied all parameters of the temp/relax and nph-fix.

I’d be grateful for any advice :>

/BR:
Gerolf

2

Gerolf,

I am assuming you are quenching your temperature to T = 0. I find that a reasonably slow quenching tends to work best in MD. Another approach for your problem could be that you build your large system out of the small system that you are able to quench (say a 4x4x4 composite of 62.5^3 A^3 units). You could then introduce some thermal randomness to the composite system by elevating the temperature slightly and running the system for a while.

Pieter

3

You could try using fix viscous which would let you run dynamics
while slowly (or quickly) quenching out the velocities.

Steve