[lammps-users] Uranium dioxide, incorrect net charge of system

Ilya_Sv1 · June 16, 2010, 8:39am

Good day everyone!

I am trying to use LAMMPS to simulate a uranium dioxide lattice.I am using Basak potential.For input into LAMMPS, I thought that the best way to implement this potential was to use pair_style hybrid/overlay to superpose pair_style born/coul/long and pair_style morse .Pair_style born/coul/long should be used in conjunction with the kspace_style command and its ewald or pppm option.I chose ewald option.

I’m new to using Lammps. I think that the easiest way to set the atomic charges of my system - the use of atom_style charge.
This is part of my input script:

#3-d UO2 simulation

units metal
dimension 3
boundary p p p

atom_style charge
latticefcc 5.4706
regionbox block 0 6 0 6 0 6 side in units lattice
create_box2 box
create_atoms1 box
lattice sc 2.73503 origin 0.5 0.5 0.5
create_atoms 2 box

mass1 238.0289
mass 2 15.9994

set atom 1 charge 2.4
set atom 2 charge -1.2

kspace_style ewald 0.0001
pair_style hybrid/overlay born/coul/long 10.0 morse 10.0
pair_coeff 1 1 born/coul/long 0.013806784 0.32702 3.26 0.0 0.0 10.0
pair_coeff 1 2 born/coul/long 0.013806827 0.327021 3.54 0.0 0.0 10.0
pair_coeff 1 2 morse 0.57745 1.65 2.369 10.0
pair_coeff 2 2 born/coul/long 0.013806869 0.327022 3.82 3.950633264 0.0 10.0

When I ran the calculation:

dir@…1956…:~/Desktop/UO2(new)> ./lmp_opensuse <in.uo
LAMMPS (7 Jul 2009)
Lattice spacing in x,y,z = 5.4706 5.4706 5.4706
Created orthogonal box = (0 0 0) to (21.8824 21.8824 21.8824)
1 by 1 by 1 processor grid
Created 256 atoms
Lattice spacing in x,y,z = 2.7353 2.7353 2.7353
Created 512 atoms
Setting atom values …
1 settings made for charge
Setting atom values …
1 settings made for charge
Ewald initialization …
WARNING: System is not charge neutral, net charge = 1.2
G vector = 0.273155
vectors: actual 1d max = 399 5 665
Ewald initialization …
WARNING: System is not charge neutral, net charge = 1.2
G vector = 0.273155
vectors: actual 1d max = 399 5 665
Ewald initialization …
WARNING: System is not charge neutral, net charge = 1.2
G vector = 0.273155
vectors: actual 1d max = 399 5 665

Why my system is not charge neutral*?*

Thank you for your attention.

sjplimp · June 16, 2010, 2:34pm

If you sum up the q value of all your atoms, you get
the system charge. It is apparently not summing to 0.

Steve

2010/6/16 Ilya Sv <[email protected]...>:

_Ahmed_E_Ismail1 · June 16, 2010, 3:18pm

2010/6/16 Ilya Sv <xadx@…1092…>

Good day everyone!

I am trying to use LAMMPS to simulate a uranium dioxide lattice.I am using Basak potential.For input into LAMMPS, I thought that the best way to implement this potential was to use pair_style hybrid/overlay to superpose pair_style born/coul/long and pair_style morse .Pair_style born/coul/long should be used in conjunction with the kspace_style command and its ewald or pppm option.I chose ewald option.

I’m new to using Lammps. I think that the easiest way to set the atomic charges of my system - the use of atom_style charge.
This is part of my input script:
set atom 1 charge 2.4
set atom 2 charge -1.2

Ilya:

The command “set atom X” changes the effect of atom X, not every atom of type X. What you want to use is the “type” keyword instead:

set type 1 charge 2.4
set type 2 charge –1.2

That will set all atoms of type 1 to 2.4, and type 2 to –1.2.

–AEI