corner atoms fly away for core-shell model

Dear Lammps users,

I am using core-shell model for Barium titanat oxide, i would like to build the model same as figure 6 in . It’s a cantilever beam, one side is fixed, the another side is free and after relaxation a downward force will apply to the free end. However during relaxation the corner atoms at the free end fly away and blowing up the temperature.

Details of my model:

1.Core-shell model for Barium titanat oxide, the core-shell requires periodic boundary for all direction. In order to study the size effect, sufficient vacuum space created around the model.

  1. temperature is applied through nvt. I also tried with temp/rescale, same thing happens.

  2. The system is not charge neutral due to free surfaces.

  3. Potential used from DOI: 10.1063/1.4827475

  4. code of relaxation:

compute temperature only for the mobile part (exclude the fixed end)

compute CSequ mobile temp/cs mobile_cores mobile_shells

velocity bias option

variable T_start equal 415

velocity mobile create ${T_start} 134 dist gaussian mom yes rot yes bias yes temp CSequ

velocity mobile scale ${T_start} temp CSequ

velocity fixed set 0 0 0

fix setforce_fixed fixed setforce 0.0 0.0 0.0

fix nve all nve

fix temp_mobile mobile temp/rescale 100 {T_start} {T_start} 1 0.5

fix mom_mobile mobile momentum 10 linear 0 0 0 angular

fix_modify temp_mobile temp CSequ

thermo_modify temp CSequ

timestep 0.004

run 1000

Any suggestion is appreciated.

Best regards

Bo

Dear Lammps users,

I am using core-shell model for Barium titanat oxide, i would like to
build the model same as figure 6 in https://doi.org/10.1103/
PhysRevB.77.125424. It's a cantilever beam, one side is fixed, the
another side is free and after relaxation a downward force will apply to the
free end. However during relaxation the corner atoms at the free end fly
away and blowing up the temperature.

​are you certain this is an effect​ of the core-shell model?
have you tried the same geometry with a non-polarizable setup?

axel.