Lammps Beginner energy minimization issue

LAMMPS LAMMPS Beginners
1

Hi, I am new to Lammps. I have been trying to use it to study dislocations in SrTiO3. The issue that I ran into was that I could not get the structure to relax. Because of that, I recently tried simplifying the structure to a cubic unit cell of SrTiO3 with the center atom shifted. Still, I can’t seem to get the structure to relax. The pair style and pair coefficients I am using are from the paper “Developing pair potentials for simulating radiation damage in complex oxides”. Additionally, when I talked to someone in my research group they said it looks like the energy does not converge.

Version of Lammps:
LAMMPS (29 Sep 2021 - Update 2)

unit cell of SrTiO3:
pymatgenunitcellshift.data (425 Bytes)
output file:
relax_unit_sto_thomas_et_al.data (557 Bytes)
log file:
pymatgenunitcellshift.data (425 Bytes)
Input File:
pymatgenunitcellshift.data (425 Bytes)

2

What does that mean?

This is way too old. Many updates have been made and its very risky to use such an old version.

You shared the same data file 3 times.

Simon

3

Thanks for your response. I have updated Lammps, and the issue persists. What I mean by relaxing the structure is performing an energy minimization to get all the atoms into their minimum energy state. So, for the unit cell of SrTiO3, I was trying to shift the Titanium in the center of my unit cell by 0.1 angstroms in the x direction, then run the minimize command. What I would expect to happen would be that the Titanium atom would return to the center of the unit cell, and all the other atoms would be in the position had I not shifted the Titanium atom. However, when I look at the output file relax_unitcell_STO the atomic positions do not match what I expect. And if I look at the structure in OVITO it also does not look like what I would expect. Also, sorry about uploading the same file three times.

input file:
input.sto_thomas_et_al.txt (1.2 KB)

log file:
log.lamps.txt (5.6 KB)

output file:

relax_unitcell_STO.txt (607 Bytes)

4

Not necessary, an energy minimization is not meant to find the global energy minimum of a system. The energy minimization step can stop simply because the atoms have moved enough to make the force/energy small enough according to the imposed criteria.

5

Since you provide only the data file(s) and not the input file, and the relevant pages from the publication you are referring to, that describe the potential function used and its parameters, it is not possible to give a meaningful assessment of the situation. The only thing that is suspicious at the moment, is that the data file does not contain any data for the (partial) charges of the atoms, but those may also be set in the input file, so this is not necessarily an error.

6

Sorry, I thought I had uploaded them, I know that can be frustrating. I have posted them below. Also thanks for responding.
Unit Cell:
pymatgenunitcellshift.data (425 Bytes)
input file:
input.sto_thomas_et_al.data (1.4 KB)
log file:
log.lammps.data (6.0 KB)
output file:
relax_unitcell_STO.data (572 Bytes)