Dear LAMMPS community,

I’m currently studying a Lennard-Jones solid (finite) sphere containing \approx 500 atoms. The interaction parameters for all systems have been set as follows: \sigma = 1, \epsilon = 1, m = 1, r_{cut} = 5.0, dt = 0.005, To preserve the free surface of the finite sphere, I’ve placed it in a large box and under NVT ensemble conditions. Then I first equilibrated the system [NVT with T = 0.3 for 5 \times 10^6 steps] at a temperature where it remains in a stable solid state.

I am interested in observing the rate of atom ejection from the sphere’s surface at a specific temperature (T = 0.4), which is higher than the sublimation temperature of this system. To accomplish this, I’ve conducted two types of simulations.

- In the first method, with the equillibrated configuration, I have fixed the system’s temperature at T = 0.4 and let the simulation run continuously for 4 \times 10^7 steps.

```
fix 1 all nvt temp 0.4 0.4 0.5
run 40000000
unfix 1
```

- The second method also involves, with the equillibrated configuration, fixing the temperature at T = 0.4; but the simulation is segmented into intervals of 2 \times 10^6 , with the total still amounting to 4 \times 10^7 steps.

```
fix 1 all nvt temp 0.4 0.4 0.5
run 2000000
unfix 1
fix 1 all nvt temp 0.4 0.4 0.5
run 2000000
unfix 1
.
.
.
```

Interestingly, the rates of atom ejection obtained from these two methods are noticeably different.

If both simulations are conducted under seemingly “identical” conditions, I would greatly appreciate it if anyone could provide insights into why such differences might be manifesting in the results.

Thank you for your help,

Bose

[I’ve attached the relevant LAMMPS input and data for your reference.]

data.np_d10_T0.3_eq_rc_5 (71.6 KB)

lj_continous.in (1.5 KB)

lj_step.in (2.5 KB)