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[lammps-users] corner atoms fly away for core-shell model
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[lammps-users] corner atoms fly away for core-shell model


From: bo He <bohe@...6615...>
Date: Fri, 18 Aug 2017 15:31:52 +0200

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.

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.

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

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

4. Potential used from DOI: 10.1063/1.4827475

5. 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