# Coulomb and buck/coul pair style

I would appreciate if you could help on my question of calculation using pair_style coul and buck/coul. I need to find the bond length of several compounds, and my input of NaCl is following:

# ---------- Initialize Simulation ---------------------

clear

units metal

dimension 3

boundary p p p

atom_style charge

# ---------- Create Atoms ---------------------

mass 1 22.99 #Na

mass 2 35.446 #Cl

pair_style coul/cut 10.0

pair_coeff * *

neigh_modify every 1 delay 0 check yes

# ---------- Run Minimization ---------------------

reset_timestep 0

#dump 1 all custom 400 dump.relax.1.* id type x y z

fix 1 all box/relax aniso 0.0 vmax 0.001

thermo 100

thermo_style custom step pe lx ly lz press pxx pyy pzz

min_style cg

minimize 1e-10 1e-10 5000 10000

However, after minimization is done, the pressure is very high as shown below

Step PotEng Lx Ly Lz Press Pxx Pyy Pzz c_eatoms

0 -21761.235 23.6 23.6 23.6 -884171.73 -884171.73 -884171.73 -884171.73 -21761.235

13 -21788.723 23.570226 23.570226 23.570226 -888647.75 -888647.75 -888647.75 -888647.75 -21788.723

Loop time of 0.802116 on 4 procs for 13 steps with 1000 atoms

I have no idea why the pressure is so high while the minimization is converged. For your information, I also attached my data file.

Would you please check this for me and let me know where I got wrong so I can fix it? Many thanks!

Best,

Siming

data_NaCl_test.MO (46.2 KB)

I would appreciate if you could help on my question of calculation using pair_style coul and buck/coul. I need to find the bond length of several compounds, and my input of NaCl is following:

i donâ€™t see any buckingham potential used in the input below, only coulomb with cutoff. that cannot work, since there is no repulsion for oppositely charged particles, they can move on top of each other and thus leading to divergence and a crash.

axel.

Hi Axel,

Thanks for your help. My buck/coul pair style is following:

# ---------- Initialize Simulation ---------------------

clear

units metal

dimension 3

boundary p p p

atom_style charge

# ---------- Create Atoms ---------------------

mass 1 24.304 #Mg

mass 2 58.933 #Co

mass 3 63.546 #Cu

mass 4 58.693 #Ni

mass 5 65.38 #Zn

mass 6 16.0 #O

# ---------- Define Interatomic Potential ---------------------

pair_style buck/coul/long 10.0 10.0

pair_coeff * * 0.0 0.1 0.0

pair_coeff 1 6 821.6 0.3242 0.0

pair_coeff 2 6 696.3 0.3362 0.0

pair_coeff 3 6 3860.6 0.2427 0.0

pair_coeff 4 6 683.5 0.3332 0.0

pair_coeff 5 6 499.6 0.3595 0.0

pair_coeff 6 6 22764.0 0.1490 43.0

neigh_modify every 1 delay 0 check yes

kspace_style ewald 1.e-6

# ---------- Run Minimization ---------------------

reset_timestep 0

fix 1 all box/relax aniso 0.0 vmax 0.001

thermo 100

thermo_style custom step pe lx ly lz press pxx pyy pzz

min_style cg

minimize 1e-10 1e-10 5000 10000

The results are

Step PotEng Lx Ly Lz Press Pxx Pyy Pzz c_

0 -20552.037 20.7 20.7 20.7 7907.1889 7907.1889 7907.1889 7907.1889

100 -20562.403 20.723425 20.723557 20.73678 786.91633 1136.4082 1140.623 83.717806

200 -20564.346 20.728921 20.72917 20.737892 401.429 639.02306 650.0531 -84.789163

300 -20565.977 20.734838 20.735478 20.739051 159.0794 274.43534 281.81439 -79.011541

376 -20568.192 20.750291 20.751315 20.747824 94.9827 -17.705675 174.78765 127.86612

Loop time of 14.1734 on 4 procs for 376 steps with 1000 atoms