CaO-CO2 reaction using reaxff

LAMMPS
, ,
1

Hi Lammps users,

I’m trying to simulate the reaction between CaO and CO2 using reaxff. I used the primitive cell of CaO to expand the cell and then created a cylindrical channel in the middle, filling it with CO2 using Packmol. However, no matter how I modify the model, the pressure always shows as nan during the minimization process. Even if the minimization process succeeds, the pressure still shows as nan after several thousand steps in the subsequent NVT simulation.

My data file and the input file are as follows,

Input

units real
boundary p p p
atom_style charge
timestep 0.5
neighbor 2.0 bin
neigh_modify every 10 delay 0 check yes

read_data fin.lmp
set type 1 charge +2.0
set type 2 charge -2.0
set type 3 charge +4.0

pair_style reax/c NULL
pair_coeff * * ffield.reax.CHO C O Ca
fix 1 all qeq/reax 1 0.0 10 1e-6 reax/c
fix 2 all reax/c/bonds 1000 bonds.reax

min_style cg
minimize 1.0e-4 1.0e-6 100 1000

velocity all create 300.0 825757 mom yes rot yes dist gaussian

thermo 100
thermo_style custom step press pe temp ke
fix 3 all nvt temp 300 500 100
dump 2 all atom 100 dump.xyz

run 4000000

Data file

HEADER

    8940  atoms
       3  atom types

  0.000000000000      59.561050000000  xlo xhi
  0.000000000000      57.493000000000  ylo yhi
  0.000000000000      61.046000000000  zlo zhi

Masses

        1   40.07800000             # Ca
        2   15.99900000             # O
        3   12.01100000             # C

Atoms # charge

     1    1   0.000000        1.230000000000       1.168000000000       1.185000000000
     2    1   0.000000        1.182000000000       3.687000000000       3.625000000000
     3    1   0.000000        3.565000000000       1.209000000000       3.573000000000
     4    1   0.000000        3.590000000000       3.605000000000       1.312000000000
     5    2   0.000000        3.713000000000       3.600000000000       3.638000000000
     6    2   0.000000        3.633000000000       1.124000000000       1.152000000000
     7    2   0.000000        1.125000000000       3.666000000000       1.240000000000
     8    2   0.000000        1.165000000000       1.263000000000       3.577000000000
     9    1   0.000000        5.943000000000       1.183000000000       1.313000000000
    10    1   0.000000        6.004000000000       3.684000000000       3.593000000000
    11    1   0.000000        8.365000000000       1.273000000000       3.602000000000
    12    1   0.000000        8.371000000000       3.611000000000       1.228000000000
    13    2   0.000000        8.396000000000       3.593000000000       3.600000000000
    14    2   0.000000        8.348000000000       1.107000000000       1.197000000000
    15    2   0.000000        5.978000000000       3.694000000000       1.237000000000
    16    2   0.000000        6.071000000000       1.249000000000       3.686000000000

……
8641 3 0.000000 26.806000000000 35.156000000000 34.617000000000
8642 2 0.000000 25.918000000000 35.522000000000 33.885000000000
8643 2 0.000000 27.695000000000 34.791000000000 35.348000000000
8644 3 0.000000 52.560000000000 37.948000000000 16.923000000000
8645 2 0.000000 52.284000000000 38.234000000000 15.782000000000
8646 2 0.000000 52.835000000000 37.662000000000 18.064000000000
8647 3 0.000000 22.005000000000 42.718000000000 31.317000000000
8648 2 0.000000 22.132000000000 42.579000000000 30.124000000000
8649 2 0.000000 21.877000000000 42.858000000000 32.510000000000
8650 3 0.000000 1.898000000000 41.753000000000 20.749000000000
8651 2 0.000000 2.258000000000 40.826000000000 20.063000000000
8652 2 0.000000 1.539000000000 42.679000000000 21.436000000000

2

I suppose the problem could be because you are adding the CO2 molecules very close to one another (or to the CaO ions) with Packmol. In scenarios where the minization works, it could be worth maybe doing some MD at a lower temperature and go progressively increasing it so that you can ultimately have a more reasonable configuration to carry out the dynamics at a higher temperature. Alternatively you could maybe add these molecules in another fashion - one that allows to add the molecules respecting a threshold of minimal distance from other existing molecules and Ca2+ and O2- ions.

Maybe the problem could also be coming from the fact that you have caved a cylinder in the CaO? I wonder if the force field you are using is suitable for simulating a “finite” (i.e., not bulk) version of the material.

3

Thank you for your response. I am using ReaxFF for a Water/Ca-OH system. After a successful minimization, I observed in the dump file that when CO2 comes into contact with CaO, the entire system disappears. What could be causing this?