# Particle phases default option

**URL:** <https://pybamm.discourse.group/t/particle-phases-default-option/218>\
**Category:** Models\
**Created:** [5 March 2025 11:31 UTC](https://pybamm.discourse.group/t/particle-phases-default-option/218 "2025-03-05T11:31:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![fmaletic](https://avatars.discourse-cdn.com/v4/letter/f/5f9b8f/32.png) [@fmaletic](https://pybamm.discourse.group/u/fmaletic)\
**Post date:** [5 March 2025 11:31 UTC](https://pybamm.discourse.group/t/particle-phases-default-option/218/1 "2025-03-05T11:31:01Z")

</div>

Hi,

I’ve noticed that there is a difference in simulation results when using

```
"particle phases": ("1", "1")

```

and with the default option, which, from what I understand from the source code, is just

```
"particle phases": "1"

```

Why is that, shouldn’t the two scenarios be equivalent?

MWE:

```
import pybamm
import matplotlib.pyplot as plt

model1 = pybamm.lithium_ion.SPMe()
model2 = pybamm.lithium_ion.SPMe(options={"particle phases": ("1", "1")})
sim1 = pybamm.Simulation(model1)
sim2 = pybamm.Simulation(model2)
sim1.solve([0, 3600])
sim2.solve([0, 3600])

fig, ax = plt.subplots(1, 1)
ax.plot(
    sim1.solution["Time [min]"].data, 
    sim1.solution["Battery voltage [V]"].data,
    label="Ub - model1"
)
ax.plot(
    sim2.solution["Time [min]"].data, 
    sim2.solution["Battery voltage [V]"].data,
    label="Ub - model2"
)
ax.set_xlabel("Time [min]")
ax.set_ylabel("Voltage [V]")
ax.legend()
plt.show()

```

---

<div class="post-metadata">

**Author:** ![valentinsulzer](https://yyz2.discourse-cdn.com/free1/user_avatar/pybamm.discourse.group/valentinsulzer/32/9_2.png) [@valentinsulzer](https://pybamm.discourse.group/u/valentinsulzer)\
**Post date:** [11 March 2025 00:29 UTC](https://pybamm.discourse.group/t/particle-phases-default-option/218/2 "2025-03-11T00:29:23Z")

</div>

That is weird, they should definitely be the same